School Science Lessons
UNPh35.1
2018-11-05
Please send comments to: J.Elfick@uq.edu.au

35.1 Geology

Websites: Geology, earth sciences

Table of Contents

See: Geology, (Commercial)

See: Models, (Commercial): Calcium carbonate, Calcium fluoride, Copper oxide
Diamond, Graphite, Quartz, Sodium chloride, Zeolite, Zinc sulfide

35.5.0 Fieldwork

35.7.0 Rocks

35.3.0 Ores

35.14.1 Silicates

Concrete

35.22.4.0 Clay
35.22.4.0 Clay
5.39 Clay, Make clay pots (Primary)
7.6.1 Clay soils in water
3.58 Clay soil suspension
7.6.3 Clay suspensions in a centrifuge
35.22.4.8 Armenian clay
35.22.4.4 Bentonite
35.22.4.9 Celadon
35.22.4.01 Chemical weathering reactions
35.22.4.5 Fuller's earth
35.22.4.7 Halloysite
35.22.4.1 Illite
35.20.21.1 Kaolinite, kaolin-type clays
7.6.2.1 Lime water with clay suspension
35.22.4.3 Montmorillonite (smectite)
7.6.2.2 Potassium alum or aluminium sulfate with clay suspensions
35.22.4.10 Pozzolana (puteolanum)
35.22.4.11 Roman Maritime Concrete Study (ROMACONS)
7.6.2 Salts with clay suspension
6.6.0 Soil particle size
3.65 Strengths of mud, clay and sand bricks
35.22.4.6 Vermiculite

35.5.0 Geology fieldwork
35.33.2 Aragonite
35.1.4 Geology fieldwork, what you will need
35.34.1 Dendrites, false fossils
35.1.1 Dip and strike, direction of a stream
35.1.3 Examine minerals and rocks
35.30 Examine sand with a magnifying glass
35.29 Faults
35.35 Find fossils
35.27 Folds
35.34 How fossils form
35.40.2 Isostasy models
35.28 Joints
35.40.1 Mapping contours, geological structures, erosion
35.30.1 Quicksand
35.32 Sort sediments
35.31 Tests for limestone
35.1.2 Visit an outcrop or quarry, lode

35.7.0 Rocks
Rocks, major groups of rocks, geological processes of rock formation
18.0 Rocks, Soils and rocks (Primary)
35.21.0 Igneous rocks
35.23.0 Metamorphic rocks
35.22.0 Sedimentary rocks

35.21.0 Igneous rocks
35.21.0 Igneous rocks
35.21.3.1 Apatite
35.21.1 Basalt
35.21.8 Classify igneous rocks in hand specimens
35.21.2 Granite
35.21.01 Igneous intrusions, batholith, dyke, sill
35.24 Make igneous rocks, alum crystals, sulfur crystals
35.21.5.1 Obsidian, perlite
35.21.3 Pegmatite, beryl, topaz, tourmaline, zircon
35.21.5.2 Porphyry
12.16.6 Prepare volcanos with baking soda
35.21.4 Pumice
35.21.5 Rhyolite
35.2.4.1 Scoria
35.21.6 Serpentine
35.21.7 Tuff, tephra

35.23.0 Metamorphic rocks
35.23.0 Metamorphic rocks
35.23.2.1 Amber, C12H20O, succinite
35.23.01 Classify metamorphic rocks
7.2.2.11 Carbon, C
35.26 Make metamorphic rocks
35.23.3 Marble, CaCO3
35.23.4.1 Oil shale and fracking, (hydraulic fracturing)
35.23.4 Petroleum, crude oil
35.23.5 Quartzite, SiO2
35.23.6 Slate (C + clay, mudstone, shales)
35.23.7 Talc, soapstone, talcstone, steatite, French chalk, Mg3Si4O10(OH)2, or MgSi8O20(OH)4
35.23.1 Coal
35.23.2 Graphite, diamond, "lead pencil", C
35.26 Make metamorphic rocks

7.2.2.11 Carbon, C
7.9.4.2 Allotropes, sulfur, carbon
35.41.1 Carbon, charcoal blocks
35.23.1 Coal, airborne coal dust explosions
35.41.2 Diamond
35.41.3 Graphite
35.41.4 "Lead pencils"
35.41.5 "Aquadag"
Jet black

35.22.0 Sedimentary rocks
35.22.0 Sedimentary rocks
35.22.6.1 Alabaster
35.22.10 Arenaceous rock, arenite
35.22.11 Argillaceous rock
35.22.2 Breccia
35.6.0 Chalk
35.22.4.0 Clay
35.22.5 Conglomerate (puddingstone)
35.22.6 Gypsum (calcium sulfate) plaster of Paris
3.67 Tests for strength of plaster of Paris bricks:
35.22.7 Limestone, stone dust, carving stones
35.22.7.1 Calcium carbonate dissolves in rain water
35.25 Make sedimentary rocks
35.22.8 Mudstone, siltstone, marl, loess
35.22.1 Sandstone
35.22.9 Shale

35.6.0 Chalk
See: Chalk rock mineral, (Commercial)
35.22.3 Chalk, Breccia, Geology)
6.43 Chalk (lime) content of the soil, (Agriculture)
Blackboard chalk, school chalk (Chemistry)

35.3.0 Ores and ore bodies
2.6.0 Free element metals
35.3.04 Froth flotation
35.3.0 Ores and ore bodies
35.3.03 Placer deposits
35.3.01 Primary ore deposits
35.3.02 Secondary ore deposits

35.14.1 Silicates
Silicates group, polysilicates, polysilicon
Silica, SiO2, silica gel, silicon dioxide
Silicates, -(SiO4)
Silicic acid, silicon oxyacid, metasilicic acid, H2SiO3
Silicon, Si
Silicon compounds
35.14.1 Silicates group, polysilicates, polysilicon
35.14.2 Opals, SiO2.nH2O
35.14.2.1 Opal valuation
35.14.3 Amethyst
35.14.4 Chalcedony

35.1.1 Dip and strike
Direction of a stream
See: Clinometer (Commercial)
See: Compass (Commercial)

See diagram 5.1.1: Dip and strike, direction of a stream
When sediments form, the particles may just drop down or be transported by wind or wave action, leaving behind a characteristic
structure when the sediments become rock.
A bedding plane is a surface of deposition, e.g. shales split along bedding planes.
Bedding planes may have different grain sizes or colours.
Dip is the angle between the bedding plane and the horizontal.
Measure the dip in a direction perpendicular to the strike.
Strike is the direction of a horizontal line drawn on the dipping bedding plane.
The direction of a stream that became dry many years ago can be seen if one rock was in a position to prevent the movement of
another rock.

Experiments
1. Use a protractor as a clinometer with the straight line between the two 180o marks with the bedding plane of the rock surface.
Read the angle of deviation of a weighted thread from the central line on the protractor scale.
Find the line along which the dip is the greatest by pouring water on the bedding plane so that it runs down the steepest path.
Record the angle and direction of dip.
On irregular surfaces use a big book or flat piece of wood as a base plate.
2. Draw a line at right angles to the dip and measure the direction of this line

35.1.2 Visit an outcrop or quarry, lode
See: Hammers, geological hammer, (Commercial)
Collect small samples of rock and minerals from outcrops or quarries.
Get permission before entering a quarry or visiting famous geological sites.
At an outcrop or quarry look at the whole exposure then draw its general features and reference points, e.g. nearby buildings or trees.
Look for bedding in sedimentary rocks flow banding that suggests igneous rocks veins where minerals occur, e.g. quartz calcite.
Collect specimens for on-site examination laboratory tests and for a geology collection.
When using a geological hammer always wear safety glasses.
Do not damage the outcrop unduly.
Do not hammer indiscriminately at every rock you see.
Use the geological hammer only when necessary to extract a small rock or mineral specimen that will fit in the palm of your hand.
Write a number on the rock sample itself and place it in a similarly numbered bag and put a numbered piece of paper in the bag.
Draw a map or take a photograph to show where you collected the samples.
Record the dip and strike.
Sample both sides of a boundary.
Mark the drawing of the outcrop or quarry to show where you took specimens.
Examine the freshly broken surface of the rock.
Hold the hand lens steady with one hand and move the specimen with the other hand to get a good focus.
Test minerals for hardness by scratch tests.
Drag a specimen over the streak plate.
White streaks are hard to see.
Put a drop of acid on the specimen for the effervescence test.
Back in the laboratory put the specimens collected in a tray with numbered compartments.
Make your own collections of rocks.
Keep the specimens separate by putting partitions in the boxes.
Attach a number to each specimen and then paste a list on the cover of the box.
In mining, a lode is a vein of mineral or rock that leads to the main body of an ore.
Make a collection of the common rocks and minerals.

35.1.3 Examine minerals and rocks
List questions to ask about the samples.
Place two different samples together and describe similarities and differences.
In the laboratory examine samples that show fresh surfaces obtained by chipping.
Wrap samples in a cloth to prevent small chips from flying off when striking hard with a hammer.
Some rocks break along pre-existing cracks and do not show a fresh surface, so hammer the sample hard to reveal unaltered surfaces.
Compare the appearance of freshly broken surfaces with the weather worn outside surfaces of the sample.

35.1.4 Geology fieldwork, what you will need
See: Hammers, geological hammer, (Commercial)
See: LB1950-001 Inclinometer, Clinometer (Commercial)
See: Compass, Magnetic Needle, (Commercial)
Acid (dilute hydrochloric acid), or white vinegar, and eye dropper for an effervescence test,
Camera, to avoid collecting specimens and as record of the geology site,
Clinometer to measure elevation and gradients, or protractor and weighted thread, to measure angle of dip,
Compass (prismatic compass) for the direction of the strike, Copper sheet or copper coin, Write-on labels,
File, steel triangular file, for hardness test, Forceps (tweezers), Geological hammer (0. 5 kg) or carpenter's hammer,
Geological maps, Glass, window glass pieces for hardness test, Gloves, leather or canvass gloves, when hammering rock,
Magnet, Magnifying glass or hand lens, Marker pens, Nail varnish, to write on rocks, Notebook, Pencils,
Plastic bags, Porcelain streak plate or piece of unglazed porcelain or bathroom tile, Rubber bands,
Safety glasses, for when using geological hammer, Steel knife blade or folding pocket knife safer for hardness test.
Back in the laboratory, you will also need a weighing scale and measuring cylinder to measure the density of the specimen.

35.3.0 Ores and ore bodies
See diagram 35.3.0: Alteration of an ore body
An ore is a mineral containing a useful substance, usually a metal, that can be profitably extracted.
An ore body is a connected mass of ore suitable for mining and is referred to by terms such deposit, seam, lode, reef, and placer.

35.3.01 Primary ore deposits
Native metals are metals found not combined with other elements, e.g. copper, gold, mercury, platinum and silver.
Minerals may be from igneous rocks and found in faults or joints in the rocks or bedded like sedimentary rocks.
The mineral may have been concentrated in the fluids that move from the main magma into the surrounding rocks then deposited in
fissures when cooling.
Minerals with high melting points and low solubility in water, e.g. cassiterite, occur close to margins of plutonic igneous rock, e.g. granite.
However, other minerals occur farther away from the igneous source, e.g. galena, stibnite and cinnabar.
Gold may occur in veins close to an igneous rock or far away.
Quartz, as a non-valuable gangue mineral, may occur associated with the above minerals or by itself.
Iron may occur in bog deposits after being precipitated chemically by iron bacteria and large occurrences of haematite, limonite and
magnetite have been formed by metamorphism of these deposits.
Metals deposited as sulfides on the sea floor include the bedded lead, zinc and copper sulfides of Mount Isa, Queensland and the lead,
zinc and silver ore bodies of Broken Hill, New South Wales.
Most minerals occurring as primary ore bodies are the sulfides and oxides of the metals and have a metallic lustre.

35.3.02 Secondary ore deposits
Weathering of a primary ore body may lead to the production of new minerals or change the concentration of metals in it.
Oxidizing may occur above the water table because of the movement of oxygenated water through the soil, but below the water table
reducing may occur.
So the upper zone of a secondary ore deposit may contain oxides, carbonates, sulfates or hydroxides of metals above secondary
sulfides formed by reduction of earlier formed sulfates.
However, below the water table the primary sulfides and oxides are unaltered under the reducing conditions.
Deposits rich in iron may have a gossan, iron cap, at the surface.
However, even inconspicuous outcrops of an ore body may contain minerals different from the original deposits.
Deposits at Broken Hill, include silver bearing galena with sphalerite and gangue minerals formed by secondary alteration of sulfides.
Minerals that are soluble in water are found only where water is scarce, e.g. nitrates occur only in waterless deserts.

35.3.03 Placer deposits
The breakdown of the rocks and minerals by weathering and erosion may cause concentration of the more durable and dense minerals
in the beds of streams, on beaches or in lakes, placer deposits.
The most common minerals in placer deposits are gold, cassiterite, rutile, zircon, monazite, platinum, ozmiridium, diamonds, sapphires.

35.3.04 Froth flotation
Froth flotation is adsorbing chemicals or minerals on mined particles with foam to float off some minerals and leave the gangue behind.
Gangue is not the same as the overburden, the material overlying the mineral body being mined.

35.3.3.1 Bustamite
Bustamite, calcium manganese silicate, MnCaSiO6, also occurs in the galena rich lodes and has pink to orange to deep brown colours.

35.3.3.3 Garnet
Garnet, manganese aluminium silicate (Mn3Al2Si3O12), Mn3Al2[SiO4)3, garnet, spessartine, spessartite
Garnet (spessartine) manganese aluminium silicate (Mn3Al2Si3O12), is a port wine red mineral commonly associated with galena ore.
Chalcopyrite, CuFeS2: 35.20.9, (mineral)
Chalcopyrite, copper iron sulfide, occurs in veins in garnet, quartzite and garnet sandstone in ore bodies.

35.3.3.12 Coronadite
Coronadite (lead manganese oxide), originally referred to as psilomelane, is massive, stalactitic, shawls, cellular, botryoidal habit,
abundant in the upper levels of the oxidized zone and outcrop, with associated minerals, goethite, forms a matrix for secondary minerals.

35.14.0 Quartz
Quartz, silica (rock crystal, rose quartz, smoky quartz, milky quartz), SiO2
Quartz model, (Scientrific)
1. Quartz, a lattice of SiO2 tetrahedra, has translucent to white to pink to brown to grey colour, hardness 7, streak white to colourless,
glassy lustre, no cleavage, conchoidal fracture and RD 2.635, probably most common and most abundant mineral.
2. Quartz resembles pieces of glass, but it scratches glass with curved or smooth broken surfaces.
3. Quartz is resistant to weathering, occurs in light-coloured weathered rocks, e.g. sandstone, but does not effervesce with cold dilute HCl.
4. Quartz occurs in granite, pegmatite, gneiss, sandstone and quartzite, with varieties including agate, amethyst, carnelian (cornelian),
chalcedony, jasper, onyx (Greek: finger nail), opal, rock crystal, milky quartz, rose quartz and smoky quartz.
5. Purple to violet quartz is amethyst, yellow quartz is citrine and dull red carnelian chalcedony was used for making seals.
6. Quartz crystals have six-sided prisms and six-sided triangular faces on ends, but one end is usually broken where attached to a cluster.
The faces are flat, edges between the faces are sharp, and characteristic striations on the surfaces of the crystal faces.
Crystal size ranges from tonnes to a size only visible with a magnifying glass with some crystals in rock cavities.
7. Quartz is used to make glass, as abrasive in "sand soap" to remove grease from the hands and in sandblasting to smooth rough surface.
Fortune-tellers and people who think crystals have supernatural properties use quartz crystals.

Experiments
1. Note the glassy lustre and hardness of quartz specimens.
2. Quartz crystals may be piezoelectric so develops electric potential under stress.
When two crystals are struck together separation of charge in the crystal lattice can produce a very high voltage so quartz is used in
barbecue piezo-igniters.
Rub two crystals of quartz together in a darkened room and see an inner glow in the crystals.

35.14.1 Silicates
Silicates group, polysilicates, polysilicon
About 95% of the Earth's crust consists of silica and silicates.
Silicates include the following minerals:
1. Olivine, peridote, chrysolite (Mg Fe)2SiO4
1.1 Olivines, Mg2SiO4
2. Beryl, Be3Al2(SiO3)6
3. Pyroxenes, MgSiO3, e.g. augite, jadeite, diopside
4. Amphiboles, e.g. hornblende NaCa2(Mg, Fe2+ Fe3+Al)5(Si, Al)8O22(OH, F)2, actinolite Ca2(Mg, Fe2+)5(Si8O22)(OH, F)2
5. Micas KAl2(Si3Al)O10(OH, F)2
6. Talc, Mg3(Si4O10)(OH)2
7. Feldspars, KAlSi3O8
8. Quartz, SiO2
Polysilicates are both minerals and manufactured polymers in the form of sheets of the silicate group (SiO4)2-, that are used in
ceramics industries and the building industry.
Polysilicon forms as chemical vapour deposits and is used in the semiconductor industry for the manufacture of metal oxide silicon
semiconductor transistors.

35.14.2 Opals
Opals, SiO2.nH2O
See diagram 6.14.1: Opal reflection
1. Opal is similar to chalcedony, but it is a hydrous silica.
It has non-metallic lustre, white streak, not good cleavage, conchoidal fracture, white colour, vitreous lustre with colour patches,
specific gravity about 2, can scratch glass and be scratched by quartz.
2. Opal mineral has no definite atomic structure, never occurs as crystals, and has the same chemical structure as glass, SiO2.nH2O.
Opal colour is not formed from impurities or chemicals within the gemstone, but differences in molecular structure causes colours.
3. The opal molecules form in a regular symmetrical pattern, so when white light enters the opal, the molecules act as myriads of prisms,
and the light is consequently refracted out as various colours.
Opal is the product of decomposition of many different rocks and may occur in ore veins and be deposited at hot springs.
4. Australia provides the world with 95% of all precious opal in eight varieties, with Lightning Ridge the most famous source.
Before purchasing opal, it is important to understand each type and the principles of their valuation.

1. Solid light (white) opal occurs as two types, milky and crystal.
Milky opal is opaque, with the colours visible on the surface only.
Crystal opal is transparent with the colours being visible from within the depths of the stone.

2. Opal triplets consist of thin slices of opal affixed to a background of black glass.
A dome of clear quartz crystal is glued to the upper surface to protect and magnify the opal.
The opal slice is so thin that it becomes totally transparent, so the black background causes the colours to darken.

3. Opal doublets are similar in construction to triplets, but without the crystal dome.
A slice of opal is glued to a piece of black glass (or similar substance) and the actual opal is then polished.
The opal is generally thicker than a triplet, with better quality opal, so doublets are more valuable.

4. Dark (black) opals have dark colours, similar to doublets and triplets, but the dark background is a natural phenomenon.
Very rare and very valuable black opals are natural doublets with a band of colour sitting on a dark background.

5. Boulder opals are mined in Queensland, Australia, where ironstone boulders occur with thin veinlets of opal running through them.
The stones are cut as natural doublets, with part of the seam of opal as the face, and the ironstone as the natural backing.
Boulder opals have a similar appearance to black opals, but have less value.

6. Boulder opal matrix is used when the ironstone / opal amalgam is such that full boulder opals cannot be cut.
So the fine veinlets and dark ironstone are polished together.

7. Stones cut from Andamooka matrix, a white mixture of opal and porous rock, are placed in a sugar solution that soaks into the rock,
then sulfuric acid is applied to carbonize the sugar and turn it black, to give fine slivers of opal a black background like black opal.

8. Synthetic opals, developed in France, are seldom never sold in Australia because they are synthetic and have little acceptance.

35.14.2.1 Opal valuation
The three basic criteria of evaluation for all opals, light or dark in colour
1. Colour: The more red visible in an opal, the more valuable, with colour hierarchy - red, orange, green, blue.

2. Brightness: The brighter and stronger the colour, the better the quality, so bright green opal may be more valuable than dull red opal.

3. Patterns: The larger the splashes of colour, the better the quality, so "pinfire" or "sheen" patterns are the least valuable.
The ultimate pattern is the extremely rare and valuable "harlequin" with a symmetrical square checkerboard appearance.

4. Misconceptions about opals
1. Opal is not soft, it has the same hardness as glass.
2. Opal is not unlucky and was considered a stone of good fortune until a rumour spread about year 1900 by London diamond merchants.
3. Opal does not shrink in settings, does not lose its colour in the sun or snow (or anywhere), and is not affected by water.
However, triplets have been glued with a resin that does not mix with moisture causes the opal to appear cloudy.
Most triplets now have a water-resistant glue, so check this before purchasing, and always obtain a guarantee.

35.14.3 Amethyst
Amethyst is a violet blue variety of quartz (Greek: amethustos, not intoxicate), thought to be a charm against inebriety!
Amethysts exhibit dichroism for circular polarization so is optically active, chiral.

35.14.4 Chalcedony
Chalcedony is fibrous with very small crystals of quartz and the silica mineral moganite, and may be in the form of gemstones:
Agate, Aventurine, Bloodstone, Carnelian (cornelian), Chrysoprase, Heliotrope, Jasper, Onyx, Sard.
Agate is concentrically banded in crazy patterns, onyx is in flat layers, sardonyx is in the form of white and brown red bands, and
carnelian is red caused by to iron impurities.
Thunder eggs are in the form of a rock shell filled with agate.
Bloodstone occurs as an opaque or translucent mineral, bright or dark green in colour and interspersed with small red spots.

35.21.0 Igneous rocks
Igneous rocks are usually hard, tough rocks, consisting of inter-grown grains of silicate minerals.
The texture of a rock is the pattern determined by the size, shape and arrangement of grains composing it.
Igneous rocks usually have a uniform texture except the porphyries where larger crystals are embedded in a fine grained ground mass.
Igneous rocks may be granular or have no visible individual grains and may be dense and glassy.
The grains are usually angular and very irregular and interlocked.
Igneous rocks solidify from molten fluid rock, magma, that is either squeezed into subsurface spaces, intrusive rock, or squeezed out
on to the surface of the Earth, extrusive rock.
Intrusive rocks are coarsely textured because of slow cooling and extrusive rocks are fine textured because of faster cooling.

Igneous rocks can be classified as follows:
1. Light colour acid rocks, rich in silicon and aluminium, contain quartz, orthoclase feldspar, plagioclase feldspar, muscovite mica.
2. Dark colour basic rock, rich in iron and magnesium, contain biotite mica, hornblende, olivine.

35.21.01 Igneous intrusions
Igneous intrusions, batholith, dyke, sill
See diagram 35.21.01: Igneous intrusions
Molten material from within the earth may reach the surface as a lava flow or force the layers or rock aside to form a massive batholith.
Also molten material may move vertically to cut overlying layers as a dyke, usually about three metres wide, or move horizontally
between layers to form a sheet-like sill.

35.21.1 Basalt
Basalt is a black, very dense igneous rock made of quartz, potash feldspar, and other minerals, e.g. biotite mica and olivine,
containing FeO, MgO and CaO, but with low SiO2 content.
When broken, basalt shows a glittering surface with olivine seen as green particles.
The minerals forming it are minute crystals.
It cannot be split into layers.
Basalt is produced from volcanic activity as lava was thrust out of a volcano then cooled.
It hardened as it flowed down the slopes often to form great lava flows, e.g. the Deccan of India.
Basalt can form hexagonal prisms at right angles to the flow, e.g. Giant's Causeway in Ireland.
Basalt rocks were widely used to build beautiful buildings.
Note the glittering of very small crystals in a basalt specimen.

35.21.2 Granite
Granite is a coarse grain light-coloured rock formed by the cooling and hardening of feldspar, quartz, biotite and hornblende, melted by
the heat of the interior of the Earth.
Crystals in the rock may be very large or too fine to be seen by the eye.
Feldspar gives granite its distinguishing colour, red, grey or pink.
Granite is an intrusive rock and occurs in dykes, sills and plugs.
The large masses occur as a batholith, e.g. the Hong Kong islands.
Polished granite has a mirror-like sheen, so is used for interiors of buildings, tombstones, memorial columns and ornamental plaques.
Examine a specimen of granite and describe it.
Note whether the specimen feels light or heavy.
Note its general colour and what colours are seen in most of its parts.
The mix of parts is a mixture of different minerals.

Experiment
Scratch the specimen with the point of a knife and note the three main mineral components of the rock:
1. Quartz is like glass and is hard.
2. Feldspar is often cream-coloured or pink.
3. Mica is black and shiny.

35.21.3 Pegmatite
Pegmatite has irregular grain size with crystal size from less than two centimetres long to huge.
The same specimen may show a variety of crystal sizes giving a very uneven look.
Pegmatite was the last of the molten rock in the Earth to harden so it retains large amounts of steam and vapours that helped to lower
the temperatures allowing the rock to harden.
This slowing down process allowed the mineral crystals to grow to such large sizes.
Pegmatite is mainly quartz, feldspar and mica.
The following rare minerals and gems may also occur as crystals in pegmatite:
1. Beryl, Be3Al2Si6O18, green beryl is emerald and blue-green beryl is aquamarine,
2. Yellow, blue or green topaz, Al2SiO4(OH, F)2,
3. Green zircon, ZrSiO4, a silicate of zirconium,
4. Many colours or black tourmaline, Na(Mg, F)Al6(BO3)3(Si6O18)(OH, F)35 .
Tourmaline may have characteristic striations on the surfaces of the crystal faces.

35.21.3.1 Apatite
See 9.226: Teeth and toothpaste
Apatite, Ca5(PO4)3(OH, F, Cl), has usually green crystals, hardness 5, white streak, glassy or greasy lustre, poor cleavage, conchoidal
fracture and RD 3.2.
It is a phosphate mixture of three minerals with slightly different chemical compositions.
It is found scattered in many rock types, is the mineral in teeth and bones, and is a source of phosphate fertilizer.
It is often found in pegmatites.
Although found in teeth, the name has nothing to do with "appetite".
Note the colour, hardness and "licked" look of the specimen.

35.21.4 Pumice
Pumice is a volcanic glass pyroclastic lava with high silica content that cooled while still containing large quantities of gases making it
light and spongy.
The escaping gases left tiny tunnels and pits giving a cellular texture like foam in the glassy rock.
Pumice usually occurs on the tops of lava flows and pieces of pumice can float and are often washed up on beaches and called
pumice stones.
It is remarkable for its light weight and is used as a gentle abrasive to remove dirt from the hands and feet.

35.2.4.1 Scoria
Scoria (Greek: rust) (cinder) is similar to pumice but it is macrovesicular, (larger vesicles and thicker vesicle walls).
It is usually dark brown to red in colour and is formed from basalt or andesite.
It may be in the form of volcanic bombs large enough to be used for decoration in gardens.
Otherwise is used as a base in gas-fired barbecues to retain heat and absorb dripped grease, aggregate to make lighter concrete
blocks, aggregate sands for horticultural purposes and back fill around subterranean water pipes.

35.21.5 Rhyolite
Rhyolite, obsidian, rhyolite, is pure, solid, natural glass that rarely has any crystal grains.
It has a bright lustre, like artificially made glass, and is usually black.
When thin slithers are examined against the light, it is seen to be transparent or smoke-coloured.
The glass may be grey, red, or a rich brown colour with fine streaks of colour through the black.

35.21.5.1 Obsidian
Obsidian, volcanic glass, is an amorphous solid formed when material thrown from an erupting volcano cools so quickly that it does
not have time to crystallize.
Obsidian breaks like a solid lump of glass, and primitive people could chip it into knives, axes or spearheads.
Perlite is a natural mineral formed by hydration of obsidian.
It is expanded to form very light porous granules used in the horticultural industry to replace vermiculite as a light weight cover for
small planted seeds to push through and provide moisture retention.
Also, it is used for chemical spills and in cat litter.
Use cat litter for tyre traction, car oil soak, absorb moisture in garbage cans, unused rooms, refrigerators and footwear, prevent
grease fires in bottom of barbecue grills.

35.21.5.2 Porphry
Porphyry, rock with large isolated crystals of feldspar or quartz surrounded by finer feldspar crystals.
"Imperial porphyry" was the purple rock containing large crystals of plagioclase feldspar used for grand buildings in Imperial Rome.

35.21.6 Serpentine
Serpentine, Mg6Si4O10(OH)8, is an altered form of olivine formed by weathering.
It does not have a distinct crystalline form, but appears as a compact fibrous matter.
Fibrous serpentine occurs in shades of yellow.
Serpentine contains the asbestos mineral chrysotile.
The pure variety of massive serpentine is usually pale green or yellow to dark green in colour with the different tints arranged in bands.
Serpentine can be carved and turned into vases and ornamental pieces.
The serpentine group occurs as a snake-like pattern of lighter and darker green colour in weathered igneous rocks and metamorphic
rocks.
Serpentine has olive green to brown to black colour, greasy or silky lustre, compact asbestos fibres if chrysotile, no cleavage and
splintery fracture if chrysotile, hardness 3 to 35.5, streak white and RD 2.35.
Note the colour feel and lustre of a chrysotile specimen.
Some geologists say that when serpentine is newly dug out of surrounding rocks and moistened, it has a characteristic smell.

35.21.7 Tuff, tephra
Materials thrown from volcanoes, pyroclasts, fall to from layers, tephra, which, with heat form pyroclastic rock, tuff or ash flow tuff.
It is a much lighter material than lava.
It varies in size from huge volcanic bombs to volcanic dust that floats in the air long after the eruption.
The dust settles down to the Earth where it forms layers of hard rock, just as if it had been deposited by water.

35.21.8 Classify igneous rocks in hand specimens
After Al Grenfell The Australian Science Teachers Journal Vol. 32 No. 3
| See diagram 35.21.8a: Classification of plutonic rocks
| See diagram 35.21.8b: Visual estimation chart for mineral abundance in igneous rocks
Use a magnifying glass to classify magmatic rocks by texture and mineralogy.
Volcanic types and plutonic types of igneous rocks have cooled and solidified at different rates typically in different physical
environments giving different textures.
Plutonic rocks are the granites, some porphyries and other igneous unstratified crystalline rocks thought to have formed at great depth
and pressure in the earth.
Plutonic rocks have individual grains coarse enough to be individually identifiable usually >1 mm diameter.
Volcanic rocks have no visible crystals.
Classify plutonic rocks using the modification of the IUGS (International Union of Geological Sciences) classification of plutonic rocks.
Use the triangular co-ordinate system in diagram 35.21.8a.
Use diagram 35.21.8b to estimate the volumetric abundance of the major rock forming minerals.
Divide the surface and sub volcanic magma systems of volcanic rocks into two broad categories with differing flows of energy and
modes of eruption.
The magmas are:
1. blown out as pieces of ejecta or
2. erupted or intruded as units of lava stuck together.
So you can distinguish corresponding hand specimens on the presence or absence of volcaniclastic texture.
Table 1. Pyroclastic rock types
Table 2. Aphyric lava, non-fragmented volcanic rocks
Table 3. Porphyritic volcanic rocks, classification by phenocryst assemblages.
Each table can be expanded to accommodate additional volcanic rocks that may be relatively uncommon generally, but locally abundant.

Classify igneous rock hand specimens
1a Fine-grained < l. mm aphanitic (Volcanic rocks)
1b Average grain diameters > 1 mm phaneritic (Plutonic rocks), Go to 5a 5b
2a Pyroclasts present (Pyroclastic rocks), See Table 1
2b Pyroclasts absent, grains interlocked (Non-fragmental volcanic rocks)
3a Ground mass glassy (Obsidian, volcanic glass, amorphous solid)
3b Ground mass crystalline
4a Aphyric phenocrysts absent (Aphyric lava), See Table 2
4b Porphyritic phenocrysts present (Porphyritic volcanics), See Table 3
5a Medium to coarse grained (Plutonic rocks)
5b Pegmatite (>30 mm) (Pegmatite)

Table 1. Pyroclastic rock types
Rock type: Features
Agglomerate (Pyroclasts >32 mm blocks and bombs rounded pyroclasts predominant)
Volcanic breccia (Pyroclasts >32 mm blocks and bombs; angular pyroclasts predominant)
Lapilli tuff (Pyroclasts 4 to 32 mm and of any shape)
Tuff (Pyroclasts < 4 mm and of any shape)
Ignimbrite (Welded tuff, unsorted nature > 50% fragments < 4 mm pumice clasts, often flattened and with frayed terminations)

Table 2. Aphyric lava
Rock type (colour)
Mafic lava (dark coloured)
Felsic lava (light coloured)

Table 3. Porphyritic volcanic rocks
Rock type: phenocryst mineralogy (Plutonic equivalent)
Basalt: +- olivine +- +- plagioclase (Gabbro)
Andesite: plagioclase +- mafic phases (Diorite)
Dacite: plagioclase +- quartz + mafic phases (Tonalite)
Rhyodacite: plagioclase + alkaline feldspar + quartz +- mafic phases, (Granodiorite)
Rhyolite: alkali feldspar +- quartz +- mafic phases (Granite)
Trachyte: alkali feldspar + mafic phases (Syenite)

35.22 Sedimentary rocks
Sedimentary rocks are made of material from previously existing rocks broken down by mechanical and chemical weathering.
Mechanical weathering includes alternate heating and cooling, expanding ice and root penetration.
Chemical weathering includes acid and alkali salts in rainwater and groundwater, + organic compounds from decaying animals and plants.
Particles from previously existing rocks form sediments that become compacted and cemented together.
However, before these processes of rock formation, rock particles may be transported by wind or water.
Sedimentary rocks may have a banded or layered appearance, are usually less compact than igneous rocks and may be crumbly.
If you breathe on them, the added moisture may give the rocks an earthy smell.
Sediments consisting of broken particles of the parent rock are called clastic, e.g. sandstone.
Cementing agents include silica, calcium carbonate and iron oxides.
The most common minerals in the fragmented rocks are quartz, feldspar, and clay minerals.
Some sedimentary rocks were precipitated from solution, e.g. limestone, calcite and dolomite.
Sea shells and corals form sedimentary rocks from the calcium carbonate.

35.22.1 Sandstone
Sandstone is made up of grains of quartz, SiO2, with particle size up to 2 mm diameter and a texture like a sugar cube.
It may also contain other particles of feldspar, garnet, tourmaline, and flakes of mica.
It also contains substances acting as cement.
Sandstone is still used for buildings because it may be plentiful in some places, e.g. Sydney, Australia, and is easy to saw and carve.
Old sandstone buildings have a straw colour but that may be spoilt by atmospheric pollution.
Quartzite is an altered and exceedingly hard sandstone.
Use a magnifying glass to examine the sandstone in any sandstone buildings or walls in your area.

35.22.2 Breccia
Breccia has a rough, angular appearance because the stones contained within it are angular, with sharp edges.
Breccia is usually formed at the base of cliffs in mountainous regions, where there is much rough, broken stone, scree.
The scree is cemented into a hard mass with sand and clay.
Breccia has little value except as fill, but the igneous breccia of South Africa contains diamonds.

35.22.3 Chalk
Chalk, CaCO3, is a soft white limestone, containing about 98% calcium carbonate, with the remainder usually made up of quartz.
Most chalk consists of broken down skeletons of sea shells.
Flint nodules (chert), made of silica solutions within some chalk deposits are hard and brittle.
Chalk is used in industry in paints, putties, polishes, rubber, crayons and in the manufacture of cement and lime.
It is graded for sale according to colour, fineness and purity.
The white cliffs of Dover, England, are made of chalk, hence "Albion" (Latin albus, white), Greek and Roman name for Britain.
Calcium carbonate occurs in calcite, aragonite, marble, pearl, coral, egg shells, whitewash, calcimine (kalsomine) and seashells.
However, the blackboard chalk used in schools is calcium sulfate, CaSO4.2H2O.

35.22.4.0 Clay
Clay minerals are hydrous aluminium phyllosilicates, tetrahedral sheets of (Al, Si)3O4, [Al2Si2O5(OH)4)], include chlorites, illite,
kaolins, e.g. kaolinite, dickite, halloysite, and smectites, e.g. montmorillonite.
China clay (white clay), is composed of kaolin.
Pipe clay is fine white clay formerly used for tobacco pipes, pottery and leather whitening.
Clay consists of decomposed weathered rock, usually granite, or others that contain feldspar.
Pure clay is a dazzling white, has a soft, oily feel and is easily broken.
Damp clay is sticky and has a special smell.
It absorbs water and becomes plastic when wet.
Clays do not split along bedding planes, i.e. a surface parallel to the original deposition surface.
It has particle size less than 0.004 mm diameter, 1/256 mm.
Clay minerals can take up or lose water according to temperature and amount of available water.
Bole is a non-plastic clay that contains iron oxide giving it a yellow to brown colour.
Clay minerals include the following groups:
| 35.22.4.1 Illite | 35.20.21.1 Kaolinite | 35.22.4.3 Montmorillonite (smectite) | 35.22.4.6 Vermiculite |
Experiments
Collect clay samples in your region.
Make clay pots and leave them in the sun to dry.
Note which clay makes the best pot.
Examine samples of potting mix for the presence of vermiculite.

Clay is sold as:
1. Modelling clay, "Plasticine", "Plastina modelling clay"
2. Feeneys clay, based on stoneware clays with refractory grog (mainly silica and alumina) and crushed trachyte, firing range 1000oC
to 1280oC, biscuit (bisque) 1020oC minimum
3. Feeneys clay, excellent plasticity, good throwing properties, fires terracotta red at mid fire in oxidation, glazes up to 1200oC, not for
reduction or high stoneware temperatures
4. Feeneys clay, throw, hand build, slab, coil, white / cream earthenware, grey / beige cream stoneware, texture medium, firing range
1000oC to 1280oC,
5. Feeneys clay, very plastic, hand building, coiling, throwing on a wheel, texture medium, firing range 1000oC to 1280oC, general
purpose potters clay
6. Blackwattle pottery, paper clay, suitable for air drying and can be fired, decorated and glazed
7. Das, air dry modelling clay, attains hardness without firing, can be coloured
8. Crayola Model Magic, sift and pliable, lightweight and spongy after drying, air dries in 24 hours

35.22.4.01 Chemical weathering reactions
Some weathering reactions need water and some need acid to produce aluminium silicate clays.
Both types of reactions reduces the size of mineral particles with the exclusion of silicic acid.
1. Al2(OH)4(Si2O5) + 5H2O --> 2Al(OH)3 + 2H4SiO4
kaolinite + water --> gibbsite + silicic acid
2. Al2(OH)4(Si2O5) + 6H+ --> 2Al3+ + 2H4SiO4 + H2O
kaolinite + acid --> aluminium ion + silicic acid + water
3. 2KAl2(OH)2(Si3AlO10) + 3H2O + 2H+ --> 3Al2(OH)4(Si2O5) + 2K+
muscovite + water + acid --> kaolinite + potassium ion
4. 2KAlSi3O8 + 9H2O + 2H+--> Al2(OH)4(Si2O5) + 2K+ + 4H4SiO4
feldspar + water + acid --> kaolinite + potassium ion + silicic acid
5. Al2(OH)2(Si2O5)2 + 5H2O --> Al2(OH)4(Si2O5) + 2H4SiO4
montmorillonite + water --> kaolinite + silicic acid
6. 2KAlSi3O8 + 12H2O + 2H+ --> KAl2(OH)2(Si3AlO10) +2K+ + 6H4SiO4
feldspar + water + acid --> muscovite + potassium ion + silicic acid
7. 2KAl2(OH)2(Si3AlO10) + 9H2O +2H+ --> 3Al(OH)3 + K+ + 3H4SiO4
muscovite + water + acid --> gibbsite + silicic acid
8. 2Al(OH)3 + 3H+ --> Al3+ + H2O
gibbsite + acid --> aluminium ion + water

35.22.4.1 Illite, most common clay mineral, KAl4(Si, Al)8O20(OH)4, or KAl4(Si, Al)8O18.2H2O

35.22.4.3 Montmorillonite, smectite
(Al, Mg)[(OH2)Si4O10].(Na, Ca)x.4H2O
(Na, Ca)(Al, Mg)6(Si4O10)3(OH)6.nH2O
(Na, Ca)0.33(Al, Mg)2(Si4O10)(OH)2.nH2O
Montmorillonite forms from volcanic ash and occurs in Fuller's earth and bentonite, Al2Mg(OH)2[Si4O10](Ca, Na)x.4H2O.
These minerals easily exchange cations and take up and lose water, so are called "swelling clays".
It is the main component of "cat litter".
Montmorillonite is the most common nanoclay used in materials applications and can be dispersed in a polymer matrix to form
polymer-clay nanacomposite.

35.22.4.4 Bentonite
Al2Mg(OH)2[Si4, O10](Ca, Na)x.4H2O
Bentonite is composed of 80% of the clay mineral smectite and is formed by alteration of volcanic ash in marine environments, as layers
sandwiched between other types of rocks.
The smectite is usually the mineral montmorillonite.
Bentonite is often included in products to improve the water holding capacity of soil because of its water absorbing and water- retaining
properties.
Bentonite is a clay-like mineral consisting of hydrous aluminium silicate.
It is of very fine grain size, can absorb large amounts of water and has a very high plasticity.
It is used in the manufacture of colloidal solutions.
Fuller's earth and bentonite.
These minerals easily exchange cations and take up and lose water, so are called "swelling clays".
E558, Bentonite is an anti-caking agent.

35.22.4.5 Fuller's earth
Fuller's earth and bentonite, Al2Mg(OH)2[Si4O10](Ca, Na)x.4H2O.
These minerals easily exchange cations and take up and lose water, so are called "swelling clays".
Fuller's earth, a hydrated compound of silica and alumina, has a grey brown colour and a smooth greasy feel.
It is used as a filtering material to remove the basic colours of vegetable, animal and mineral oils and as a pigment filler.
Fuller's earth is a high calcium clay earth, mainly montmorillonite, used to absorb grease from raw wool, wool relaxant, shrink and
unshrink woollen clothing, decolorize, filter, purify oils and greases.
Fulling means to clean and thicken cloth by removing impurities.

35.22.4.6 Vermiculite
Vermiculite, granular form (inert material for chemical spills, cat litter, insulation, packing, potting mix), Irritating to skin and eyes.
Vermiculite, Mg2FeAl[(OH)2AlSi2O10Mg((H2O)4], or (Mg, Fe, Al)3(Al, Si)4O10(OH)2.4H2O.
It is used as a mulch and potting medium in horticulture and as heat insulating material.
Gardeners claim it can hold seven times its own weight in water and it provides good drainage in soil mixes.
The name comes from the property of forming long worm-like structures when heated.
Examine samples of potting mixes bought from different suppliers for the presence of vermiculite.

35.22.4.7 Halloysite
Halloysite, Al4Si4(OH)8O10.4H2O, clay mineral
Halloysite contains naturally occurring aluminosilicate nanotubes, with average dimensions 15 X 1000 nm.
They are hollow and so it can be used to control delivery of and release of drugs.

35.22.4.8 Armenian clay
Armenium bole, Bolus amenus, salameniacum, historically a famous red clay used as a medical astringent, book-binding filler and
waterproofing agent containing a high proportion of iron oxides and hydrous aluminium silicates.

35.22.4.9 Celadon
Celadon is an ancient Chinese ceramic, and greenish jade-like glaze from Fe2O3 --> FeO reaction.

35.22.4.10 Pozzolana (puteolanum)
Pozzolana is a powdery red volcanic ash and pumice, mainly SiO2, also aluminium hydroxide and iron salts, formerly used to make
ancient Roman pozzolana-lime waterproof concrete.
Nowadays, it is mixed with Portland cement for the pozzolanic reaction.
Ca(OH)2 + H4SiO4 --> Ca2+ + H2SiO42- + 2H2O --> CaH2SiO4.2H2O (calcium silicate hydrate)
Also, Al(OH)4- + calcium hydroxide + water --> calcium aluminate hydrate

35.22.4.11 Roman Maritime Concrete Study (ROMACONS)
Harbour walls in Caesarea, 23-10 BC were constructed from a concrete made form tuff and pozolana from the Bay of Naples.
Modern study has shown tiny crystals in ancient Roman concrete, used to construct sea walls and harbour piers, were mixture of
volcanic ash and quicklime, which may keep the concrete from fracturing and maintaining under water for so long.
Tobermorite, calcium silicatehydrate, Ca5Si6O16(OH)2.4H2O
The crystals discovered were aluminous tobermorite crystals, {[Ca4(Si5.5Al0.5O17H2)]Ca0.2Na0.1.4H2O}, growing out of
the mineral phillipsite {(Ca, Na2, K2)3Al6Si10O32.12H2O}.

35.22.5 Conglomerate
Conglomerate, puddingstone, consists of pebbles rounded by water action, cemented together by hardened clay or sand.
The pebbles are mainly quartz granite limestone and basalt.
Conglomerate occurs in the flood plains of old river valleys beaches and the outwash fans where a river joins a lake or sea.
The lower layers of these beds become compressed and cemented to form conglomerate.
The conglomerate formed by the grinding action of glaciers is called tillite.
The particles in tillite may be so fine that they are called rock flour or glacial flour.
The melting end of a glacier may show a white waterfall containing the glacial flour.
Conglomerate is seldom used as a building material because of its uneven texture.
However, very large rounded stones and small white pebbles may be extracted from conglomerate and used for decoration.

35.22.6 Gypsum
Gypsum (calcium sulfate) plaster of Paris
Calcium sulfate
Plaster of Paris
School chalk, blackboard chalk
Gypsum, CaSO4.2H2O, has white to grey colour depending on impurities, hardness 2, white streak, white to grey glassy to pearly
lustre, good cleavage in one direction, RD 2.32.
It forms from evaporation of sea water as large, in four varieties of transparently clear crystals, all called "selenite" (satin spar, desert
rose, gypsum flower), that break into plates with a glistening or pearly appearance.
So the mineral called "selenite" does not contain the atom "Selenium", Se!
Rock gypsum contains some lime and sodium chloride.
Gypsum, calcium sulfate, has a habit consisting of fibrous, massive, colourless transparent crystals.
It is located in ore bodies in the seams, cavities, water courses and crusts in abandoned workings.
The associated minerals are rosasite, linarite and dolomite.
Gypsum occurs in the beds of lakes, mixed with sand and clay washed into the depression after the formation of the gypsum.
Gypsite is an earthy surface deposit.
Satin spar is a silky fibre.
To make plaster of Paris, gypsum is heated to form the hemihydrate (2CaSO4.2H2O), then mixed with water.
It can form twin crystals.
About 4% of the mixture used to make Portland cement is gypsum.
Gypsum has low thermal conductivity so is used as a filler insulator in buildings.
Scratch the specimen with a fingernail, but note that it is not as soft as talc.
Crystals are flexible but not elastic, so they do not return to the previous shape.
The lustre is non-metallic, vitreous, also pearly or silky.
Anhydrous calcium sulfate occurs as the mineral anhydrite.
2CaSO44H2O + Heat --> 2CaSO4H2O + 3H2O
gypsum --> plaster of Paris + water

35.22.6.1 Alabaster
1. Alabaster, calcite from Alabastron, Egypt, has colour banding, used to make sealed ointment jars to be broken open before use.
In Bible, Mark 14:3, "3 While he was in Bethany, reclining at the table in the home of Simon the Leper, a woman came with an alabaster
jar of very expensive perfume, made of pure nard. She broke the jar and poured the perfume on his head."
Stalagmitic origin showing patterns similar to onyx, so also called "onyx marble", but it is not an onyx.
1. Alabaster, hydrous sulfate of gypsum, CaSO4.2H2O, occurring in a very fine grained and translucent form.
In the purest form it is snow white but it occurs also coloured due to the presence of metallic oxides.
It is found in Europe and its softness allows it to be carved into sculptures and polished for ornaments.

35.22.7 Limestone
Limestone, stone dust, carving stones
35.31: Tests for limestone
Limestone, CaCO3, is made up of the shells and skeletons of tiny organisms that once lived in the seas.
These organisms extracted calcium carbonate from the sea water and built up beautiful microscopic structures.
These sank to the seabed when the organisms died, and decayed there.
Dead organisms formed deposits thousands of feet thick.
With later earth movements, the limestone layers were uplifted and exposed above the water's surface.
Limestone is now quarried and used in the manufacture of cement.
"Stone dust" is finely crushed limestone used in coal mines to render fine coal dust incombustible and prevent underground explosions
of methane gas
Carving stones include the following:
1. "Creastone" carves like soap but hardens like stone
2. Hebel blocks are autoclaved aerated concrete
3. Limestone
4. Talc, soapstone, talcstone, steatite, Mg3(Si4O10)(OH)2: 35.23.7
5. Vermiculite (Mg, Fe, Al)3[(Al, Si)4O10](OH)2.4H2O or Mg2FeAl[(OH)2AlSi2O10Mg((H2O)4]: 35.22.4.6
When using carving stones, ball clay and glaze, a dust mask or respirator must be worn.
Dust control is important to avoid dust exposure to students in later classes.
Wet cleanup cloths must be washed before being used again.

35.22.7.1 Calcium carbonate dissolves in rain water
Rain water is weakly acidic and can dissolve calcium carbonate.
CO2 (g) + 2H2O (l) <--> H3O+ (aq) + HCO3- (aq)
H3O+ (aq) + CaCO3 (s) <--> Ca2+ (aq) + HCO3- (aq) + H2O (l)
CO2 (g) + H2O (l) + CaCO3 (s) <--> Ca2+ (aq) + HCO3- (aq)

35.22.8 Mudstone
Mudstone, siltstone, marl, loess
Mudstone and siltstone are intermediate stages between clay and shale, 1/16 to 1/256 mm diameter.
They do not split into bedding planes.
However, they do split into plates and are easily rubbed back to mud or silt if moistened with water.
They are soft and silky to touch and dissolve easily so are not often used as a building stone.
Mudstone may contain fossil impressions of plants and animals.
Marl is a calcareous mudstone.
In China, fine silt has been deposited by wind to form loess.

35.22.9 Shale
Shale splits easily into bedding planes parallel to the orientation of the clay mineral particles.
Shales do absorb water and become plastic when wet, but may disintegrate under water.
The colours are pink to yellow and brown to grey.
Shales may contain fossils and have an earthy smell.
Under great pressure, shale forms slate.
Oil shales are brown to green fine-grained shales rich in carbon-based substances.
Oil can be extracted from these light weight shales by heating.
A cut with a knife leaves a greasy mark that is darker than a freshly broken piece of shale.
Pieces of oil shales may burn with a smoky flame that smells of kerosene.
Exposed oil shales turn white and split into layers.

35.22.10 Arenaceous rock, arenite
Sedimentary clastic rocks, mostly silica, < 2 mm grain size.

35.22.11 Argillaceous rock
Contains clay minerals, aluminosilicates, and include claystones, mudstones, siltstones and shales, said to smell like rain on hot ground.

35.23 Metamorphic rocks
Metamorphic rocks are the result of heat and pressure applied to igneous and sedimentary rocks.
The pressure causes mineral grains to align in a single plane so the rock tends to split in this direction.
This alignment is called foliation.
However, marble and quartzite are metamorphic rocks but are not foliated.
Metamorphic rocks are similar to igneous rocks in that they are hard and have interlocked mineral grains.
Thermal metamorphism, contact metamorphism, is caused by heat when molten lava heats rocks to form fine grain rocks with no
bands or layers, e.g. hornfels.
Regional metamorphism refers to the changes caused by extensive heat and pressure to produce coarse grain, banded rocks,
e.g. gneiss.
The three varieties of foliation are as follows:
1. Gneissic or banded foliation shows distinct bands of different minerals.
The thicker bands are usually feldspar.
2. Schistosis foliation is caused by the parallel arrangement of platy minerals, e.g. mica.
3. Slaty cleavage refers to the tendency of a rock to split into thin, even slabs, e.g. slate.
The cleavage is the result of the parallel planar arrangement of microscopic mineral grains.

35.23.01 Classify metamorphic rocks
1. Foliated, banded or platy:
1.1 Coarsely banded, bands irregular in thickness (gneiss)
1.2 Schistose, regular banding, medium in thickness, and platy (schist)
1.3 Slaty regular fine banding and platy (slate)
2. Non-foliated, massive or granular:
2.1 Mainly calcite or dolomite (marble)
2.2 Mainly quartz - quartzite
2.3 Mainly serpentine and / or talc (serpentine or talc)
2.4 Mainly organic, grey or black (graphite and anthracite coal)

35.23.1 Coal
Coal, coal dust explosions
1. Coal is mainly carbon from woody material, algae and any plant debris that collected millions of years ago in swamps.
The heat and pressure caused by overlying deposits of sand and clay caused the formation of coal.
The older the coal the greater the percentage of carbon.
Peat is a lowest quality coal.
It has a high percentage of water.
Lignite or brown coal is older than peat and has received much more compression.
Bituminous coals are hard, black and brittle.
Anthracite ( Greek: anthrakitēs, glowing coal) is black and shiny.

2. Coal expert market
The Australian coal export market divides coal into two classes:
2.1 Metallurgical coal, which is used to make steel.
1 tonne of metallurgical coal + 1.95 tonnes off iron ore produces 1.3 tonnes of steel.
Metallurgical coal includes
Semi-Soft coking coal (SSCC)
Hard Coking Coal (HCC)
Coal Injection coal (PCI), which can also be used for thermal power generation
2.2 Thermal coal, which is used to produce electricity.
1 tonne of thermal coal produces 3 megawatts of electricity.

3. Coal dust explosion
A coal dust explosion occurs when a concentration of coal dust is lifted and ignited.
Ignition of a small quantity of methane gas in a coal mine generates a pressure wave that can lift coal dust and ignites it.
Unless the reaction is limited, the coal dust will continue to lift and burn and create an even larger pressure wave so that a coal dust
explosion occurs throughout the coal mine.
Such explosions can be prevented in two ways:
3.1 Eliminate both ignition sources for methane from electrical equipment or frictional sparking and eliminate accumulations of methane
by ventilation.
3.2 Prevent accumulation of fine coal dust and make inert coal dust accumulations by stone dusting, i.e. application of finely crushed
limestone, called stone dust, to make the fine coal dust incombustible.
Also, by storing stone dust as passive explosion barriers, any explosion causes dispersal of the stone dust to make the airborne dust
cloud incombustible.

Experiment
Collect different types of coal and break them with a hammer.
You may find fossils in the peat and softer coal.
Anthracite breaks with a conchoidal (shell-like) fracture similar to when you smash the corner of a piece of glass.
Find the weight and volume of the coal samples and calculate the density Burn the coal samples to heat waters and estimate that sample
produces the most heat per gram of coal.

35.23.2.1 Amber
Amber, C12H20O, succinite
Amber (substance, smell, colour)
Amber (Arabic: anbar ambergris) is a fossil residue in sedimentary rocks from extinct coniferous plants from the Eocenic period,
colourless to apple green to brown, greasy lustre, transparent to translucent, hardness 2-2.5, RD 1.0 to 1.1, conchoidal fracture,
brittle, produces electrostatic charge when rubbed, amorphous non-crystalline, in gravel.
Formerly found on the Baltic Sea coast where cutting and pressure moulding used to make ornamental objects.
Bakelite was first produced to make imitation amber.

35.23.3 Marble
Marble, CaCO3, is a crystalline limestone formed by the heating of limestone rock under pressure, thermal metamorphism.
If limestone is heated strongly, it gives off carbon dioxide leaving quick lime, calcium oxide, CaO.
If limestone is heated under great pressure it melts and does not lose carbon dioxide.
If it then cools slowly, it recrystallizes as marble.
Marble is a beautiful building stone, valued for its smoothness and hardness.
Pure white marble is recrystallized calcite and looks like a sugar cube.
Different colours in marble are caused by impurities, e.g. dolomite, silica, iron, clay minerals.
Not all polished stones are marbles
A common method of preparing carbon dioxide is to add hydrochloric acid to marble chips.

35.23.4 Petroleum
Petroleum
Petroleum consists of crude oil and gas.
Crude oil is mostly hydrocarbons with some oxygen, nitrogen and sulfur.
The latter may increase the expense of refining.
Most scientists think petroleum was formed from the decomposition, heating and burial of organic matter at great depths often of
marine organisms.
However, some people suggest an inorganic origin.
Oil deposits usually occur in sedimentary rocks with a thick layer of rock above and below.
The oil may float on a layer of water and be under a layer of natural gas, a mixture of gaseous hydrocarbons, mainly methane.
Crude oil is usually a dark green, brown or black oily liquid with a characteristic smell.
It always occurs with gas and water.
A waxy form of petroleum is made from coal.

35.23.5 Quartzite
Quartzite is an altered and exceedingly hard sandstone.
The grains have been bound together by a cement formed by the dissolving action of heated water.
The constituent grains have been recrystallized to form dense interlocked cementation.
When sandstone is broken, only the cement holding the sand grains together is damaged.
If a piece of quartzite is shattered, both the sand grains and cement are broken because the particles are so strongly bound together.
Quartzite has a glistening appearance caused by its sugar-like crystal structure.
Quartzite is white when pure, but most of it contains mica, iron, feldspar or other mineral particles that alter the colour to grey, brown,
red, yellow, green or black.
Owing to its extreme hardness, quartzite has few uses except for road making.
Citrine, SiO2, yellow, colour variety of quartz, vitreous greasy lustre, hardness 7, RD 3, translucent, conchoidal fracture.

35.23.6 Slate
Slate is a dense rock with a texture so fine that the individual grains in it cannot be seen by the eye or even through a magnifying glass.
Slate comes from clay, mudstone and shales altered by heat and pressure.
It was once laid down as alluvial material at the bottom of lakes and oceans.
Fossils of long dead marine plants and animals can be seen perfectly preserved in it.
Most slate is grey, dark grey or black, depending on how much plant material it contains.
It may also be green because of the chloride in sea water, or red, purple, yellow or brown because of iron stains.
Slate has a well-marked cleavage so the surface of the flat broken piece of slate feels soft and silky.
Although easily cut, slate resists the weather so it is for roofs.
Formerly, school children learnt their lessons on small slate boards that they could write on with chalk and later erase the writing.

35.23.7 Talc
Talc, soapstone, talcstone, steatite, French chalk, Mg3Si4O10(OH)2, or MgSi8O20(OH)4, "magnesium silicate"
| Talcum powder, talc, baby powder | E553b Talc
Talc has green to yellow to white colour, hardness 1, white streak, pearly to greasy lustre with a silvery sheen, good but not visible
cleavage, occurring in plates or granular form, greasy to touch, RD 2.7 to 2.8.
Talc forms as a secondary mineral after metamorphosis.
Pieces of talc break into distinctly thin, easily bent layers that remain in that shape.
So talc is flexible but not elastic.
Talc occurs as compact masses, not crystals.
Talc is used to make talcum powder, dry lubricants, fireproof materials, linoleum, paper filler, a filler in glazing and in cosmetics and
floor coverings.
Soapstone is a compact form of talc used for carving.
Tailors use small pieces of talc, French chalk, to mark cloth.

Handle a talc specimen and note that it has a pearly surface, is greasy to touch, and can be easily scratched by the fingernail.
Use it to mark paper.

35.24 Make igneous rock
Make igneous rocks, alum crystals, sulfur crystals
Crystallization of alum solutions is similar to the formation of coarse-grained and fine-grained igneous rocks.
1. Alum
1.1 Fill a test-tube one quarter full of powdered potash alum, [Al2(SO4)3.K2(SO4).24H2O], or [KAl(SO4)2.12H2O].
Slowly add just enough boiling water to dissolve the alum.
Hold the test-tube in a flame so that the mixture boils gently.
1.2 Pour half the solution into a shallow metal container.
Place a piece of string partly in the liquid and add a seed crystal.
Stir the alum solution in the container so it cools quickly.
1.3 Hang another piece of string in the test-tube so that it reaches the bottom and add a seed crystal.
Place the test-tube where it will cool slowly.
Examine the two solutions the following day and note the sizes of the crystals formed.

Sulfur
2. Melt some sulfur in a test-tube.
Fit a filter paper into a funnel and pour the molten sulfur into it.
As the sulfur cools it begins to solidify, first forming a crust on the surface.
As soon as the crust has formed, remove the filter paper from the funnel and unfold it, so that the still liquid sulfur in the lower part of
the filter can flow away from the crust.
Note a mass of small crystals on the underside of the crust.
Use a magnifying glass to observe the shape of these crystals.

3. Melt sulfur
Melt sulfur in a test-tube then pour it into a large beaker of water so that it solidifies rapidly to form plastic sulfur.
Take it out of the water and examine it after two hours.
The solid sulfur formed is very hard and you cannot see crystals with a magnifying glass.
However, very tiny crystals may be seen with a microscope.

35.25 Make sedimentary rocks
1. Use a hammer to grind different coloured sedimentary rocks, keeping the colours separated.
Put coloured powdered particles in a glass jar as different layers.
Let water trickle down the inside of the jar so as not to disturb the layering until the water is 1 cm above the sediments.
Put the jar in the sun and let the water evaporate.
Wrap the jar in a thick cloth and break it with a hammer.

2. Mix Portland cement
Mix Portland cement with water and put it in a mould until it hardens.
Break the set cement with a hammer and examine the outside and inside surfaces.

3. Mix dry cement with twice as much sand or gravel to form concrete.
Add water, mix thoroughly, and place it in a mould.
Leave the concrete to harden for several days.
Break the set concrete with a hammer and examine the outside and inside surfaces.
Note whether the concrete is easier or harder to break than the Portland cement.

4. Mix plaster of Paris
Mix plaster of Paris with a small amount of water and put it in a mould until it hardens.
Stir rapidly or it will harden while being mixed.
Break the set plaster with a hammer and examine the outside and inside surfaces.
Note whether the plaster is easier or harder to break than the Portland cement or the concrete.

35.26 Make metamorphic rocks
Fire a shaped piece of clay that has first been dried and put on a piece of broken pottery.
Heat the shaped clay in a large crucible over a Bunsen burner.

35.27 Folds
See diagram 35.27: Folds
Folds occur where parallel layer form an arch (anticline), or form a trough (syncline).
The line along which the direction of dip changes is the hinge line.
Arrange carpets or blankets in layers on the floor.
Push the layers horizontally to create anticlines and synclines.

35.28 Joints
Joins are fractures in rocks where no relative movement occurs each side of the fracture.
Joints can be caused by cooling shrinkage and increased tension within the rock.

35.29 Faults
See diagram 35.29: Faults
A fault is a fracture in rock where some displacement has occurred.
The fault plane of the fracture can be vertical but usually there is a dip of the fault.
Dip-slip movement is where the direction of movement on the fault plane, is parallel to the dip of the fault, i.e. up or down.
Strike-slip movement is where the direction of movement on the fault plane is parallel to the strike of the fault, i.e. sideways.
This movement results in tear faults.
The throw of a fault is the vertical displacement between blocks of rock.
The heave of a fault is the horizontal displacement of blocks of rock.
The hanging wall is the surface with rock above it.
The footwall is the surface with rock below it.
A normal fault is a dip-slip fault with the hanging wall on the downthrow side, i.e. it appears that a block has slipped down the fault.
A reverse fault is a dip-slip fault with the hanging wall on the upthrow side, i.e. it appears that a block has been pushed up the fault.
A trough fault is caused by downthrow movement between two parallel faults to form a graben or rift valley.
Upthrow between two parallel faults results in a horst.
A series of parallel faults is called step faulting.
Make layers of modelling clay, Plasticine.
Cut the layers vertically then cut the layers at an angle to create a model of a fault.

35.30 Sand
Examine sand with a magnifying glass
The nearly colourless crystals are probably the mineral quartz.
Look for other minerals in the sand.

35.30.1 Quicksand
Areas of quicksand have a source of upwards pressure from a spring below.
The sand becomes suspended and frictionless so will not support weight on it.
A person caught in quicksand should try to float on the back and keep the arms below the surface.
The nose and mouth should remain above the surface and allow a slow and labourious paddling to the edge of the quicksand.

35.31 Tests for limestone
Calcium carbonate
Drop lemon juice, or vinegar, or dilute hydrochloric acid on rock specimens.
Limestone will effervesce or bubble caused by carbon dioxide gas given off.
Marble, a metamorphic rock made from limestone, will also respond to this test.

35.32 Sort sediments
Thoroughly mix equal portions of gravel, coarse sand particles, and clay particles.
Place this mixture in a glass jar, not more than half full.
Fill the jar with water.
Place a cap on the jar and shake vigorously.
Allow the material to settle.
The components will arrange themselves in order, with the heavier particles at the bottom and the clay particles on the top.

35.33.2 Aragonite
Aragonite, CaCO3, calcium carbonate (pea stone in hot springs), shows dimorphism.
Aragonite and calcite are the two polymorphs of calcium carbonate, CaCO3.
Aragonite has orthorhombic crystals with repeated twinning in "pseudo-hexagonal form", i.e. the angle is 63o48' instead of 65o, to form
flower-like aggregates, "flos-ferri", flowers of iron.
Carbonates of cadmium, iron, magnesium, manganese, zinc, and double carbonates of calcium and magnesium are isomorphous with calcite.
However, the carbonates of barium, lead, and strontium are isomorphous with aragonite.
Sodium nitrate crystals are isomorphous with calcite but potassium nitrate crystals are isomorphous with aragonite at room temperature,
but changes to the calcite form at high temperature.
Aragonite forms in the shells of molluscs and freshwater corals.
Fossil coral shells, ammolite, is an iridescent gemstone.
Agagonite forms unusual stalactites in some caves.

35.34 How fossils form
A fossil is any evidence of a form of life that lived some time in the past.
Most fossils are found in layers of sedimentary rock.
Fossils formed by burial are usually found when the sedimentary rock containing them is split open.
Cover a leaf with petroleum jelly and place it on a pane of glass or other smooth surface.
Make a circular mould about 2 cm deep and place it around the leaf.
Hold the mould in place by pressing modelling clay around the outside.
Now mix up some plaster of Paris and pour it over the leaf.
When the plaster has hardened, you can remove the leaf, and you will have an excellent leaf print.
Some fossils were made this way by having silt deposited over them, which later hardened into sedimentary rock.
Repeat this experiment using a greased clam or oyster shell to make the imprint.

35.34.1 Dendrites, false fossils
Manganese and iron oxides and hydroxides may form deposits branching through limestone, dendrites.
These branches may be mistaken for fossils, but they are only chemical in origin.

35.35 Find fossils
In some localities, fossils may be found in stone quarries or where there are rock outcrops.
Try to find someone in the community who knows about fossils and then plan a field trip with the class to collect some of them.
If there are no fossils in your locality, you may have to depend on state or national museums to send you a few.
A letter to the state or national museum may prove helpful.

35.40.1 Mapping contours, geological structures, erosion
After N.E. Austin The Australian Science Teachers Journal Vol. 33 No. 1
See diagram 35.40.1: Contour lines
1. Show relief on the map with contour lines.
To develop skills in contour line interpretation by experimental means use landform models of the three fundamental surface forms:
1.1 planar,
1.2 concave, and
1.3 convex.
They exist in five spatial forms as in figure 1. A.
Make the five forms A to E from flexible white cardboard.
Contour lines are lines joining places of equal altitude, i.e. for small regions of the Earth's surface the intersection of equally-spaced
horizontal planes with the Earth's surface.
For landform modelling, you can produce such planes with plastic sheets held vertically or 35 mm slides, e.g. S1 and S2 as in figure 2,
with the back light or projector projecting horizontally.

2. Project S1 horizontally on the five spatial surface forms A to E then look vertically down on to the models.
You can vary the inclination of each of the models A to E from 10o to 90o.
Also you can vary the concavity or convexity of models B to E if the white cardboard used to make them is flexible.
The figure 3 shows what you see when looking vertically down using S1. In A B and C contour lines are straight lines on all surfaces
that can be generated by the translation in space of any horizontal straight line moving parallel to itself.
In D and E contour lines are curved on all surfaces that can be generated by translation in space of any straight line inclined to the
horizontal moving parallel to itself along a curved path.

3. Figure 4 shows what you see when looking vertically down using S2. In A B and C contour line spacing decreases with increasing
steepness of the landform.
Figure 3D and figure 4D show that if contour lines are concave when viewed from the direction of low altitude to high latitude the
landform is concave.
Figure 3E and figure 4E show if contour fines are convex when viewed from the direction of low altitude to high altitude the landform is
convex.
The same spatial forms described above can be used in developing concepts of outcrop in relation to geological structures as in figure 35.
In these experiments, the projector can be positioned to take into account varying orientations of geological structure and landform.

35.40.2 Isostasy models
After N.E. Austin The Australian Science Teachers Journal Vol. 32 No. 3
See diagram 35.40.2: Isostasy models
1. Make a tank from acrylic or glass sheet.
Keep a clearance of 2 mm at the sides and ends of the tank.
Make a water inlet at the base of the tank to help filling and draining with a garden hose.
Adjust the mass of wooden blocks of various lengths by inserting rolled lead sheet and float the blocks in a water tank,
e.g. use 50 mm × 25 mm redwood timber density 0.6 g cm-3.
Cut a basic length 38 cm long.
Calculate its true volume, V.
Multiply this volume by 0.7 to find its adjusted mass M.
Drill a 9 mm hole centrally upward through the base.
Cut a short length of 9 mm dowel to act as a sealing plug in this hole.
Put rolled sheet lead in the hole to adjust the RD to 0.7.
Put on a balance the 38 cm block, the prepared plug and the rolled lead sheet to bring total mass up to the calculated adjusted mass.
Use lead shot in the final mass adjustment.
Insert the prepared lead in the prepared hole after rolling the sheet to fit.
Glue in the prepared plug.

2. Airy's model
To make an Airy's model cut 15 lengths of the redwood timber between 38 and 19 cm long.
Drill and prepare plugs as above.
Calculate the adjusted mass M for each length as above or use formula: Ma LM / 38 where L length in centimetres, M mass of density
adjusted 38 cm basic length in grams.
Adjust all lengths as before.
Check all lengths in a one litre measuring cylinder of water by flotation.

3. Pratt's model
To make a Pratt's model cut the same number of lengths are cut as before.
The shortest possible length now is 28 cm so cut the lengths cut are between 38 and 28 cm.
Prepare all drilled lengths and plugs.
Use a longer drill hole for short lengths because you must adjust all lengths to the same mass M of the basic adjusted 38 cm.
The shorter the length the greater the RD.

4. Erosian block
To make an erosion block cut a 38 cm length of 100 mm × 50 mm timber.
Cut away the top corners of this block using a fine saw.
Join the off cuts back together using an aluminium plate.
Replace this block in its original position and drill the plate and whole block for a suitable locating pin.
Adjust this whole block to a RD of 0.7 as above.
Introduce the larger erosion block into the Airy model.
Remove the four shortest blocks from this set and introduce this block near the centre of the array.
Remove the cut away upper corner block to simulate erosion and observe the isostatic readjustment.
Replace this cutaway to simulating snowfalls and observe the isostatic readjustment.

35.41.1 Charcoal blocks
Charcoal blocks are hazardous in one way only: they smoulder and burn for a long time after ignition and may cause fires if put away
before they have been properly extinguished.
They have caused fires in schools.
If charcoal blocks are hastily collected and put in a drawer or cupboard after a laboratory class, they may smoulder for hours or days
before either extinguishing themselves or flaring up.
At the end of a laboratory class, leave the blocks totally immersed in a bucket of water.
An alternative to using charcoal blocks is to mix equal volumes of metal oxide and charcoal powder in a test-tube and heat with a
Bunsen burner while the tube is held horizontally.
Charcoal can be produced by charring bread with a Bunsen burner in a fume cupboard.

35.41.2 Diamond, C
See: Models, inorganic, Diamond, 30 "atoms", (Commercial)

Diamond
Diamond has strong covalent bonds in three dimensions to four other atoms, is colourless, transparent, brittle and non-conductor.
Diamond is crystallized carbon but it is one of the hardest minerals.
It is used as gemstones, diamond dust abrasives and rock boring tools.
Diamonds are ground into a powder by micronization with a fluid that breaks down the solid diamonds into powdered form to produce
tiny grains of the same size.
Diamond powder is graded from 0.25 microns to 50 microns.
Uniformity of the diamond particles are important for diamond powder super abrasives because irregularly shaped diamond grains may
scratch a material instead of polishing it.
For evenly-shaped particles such as synthetic diamonds, the spherical volume is similar to the calculated ellipsoidal volume because the
average length and width of the particles are nearly equal.

35.41.3 Graphite
See: Models, inorganic, Graphite, three layer, 45 "atoms", (Commercial)
1. Graphite powder (1-2 micron), colloidal, in oil solution to coat pith balls to give a conducting surface, dry lubricant.
Graphite has covalent bonds that are strong in one dimension but weak between layers, has density 3.5, and is soft and black.
slippery with lustre and is good conductor only along its layers, available as graphite mineral, graphite powder and colloidal graphite.
Graphite, like diamond, consists of the crystallized carbon, C.
Graphite has metallic lustre, can mark paper, grey to black colour, black streak, cleavage in one direction, and RD 2.1.
It occurs in crystalline igneous and metamorphic rocks and is also made artificially by heating coke in a furnace.
By contrast diamond is crystallized carbon but it is one of the hardest minerals and is colourless and transparent.
Graphite occurs in crystalline igneous and metamorphic rocks and is also made artificially by heating coke in a furnace.
The form of graphite called "blacklead" is used in pencil "leads", and was used for polishing fire grates.

2. Graphite is a good conductor of electricity, but diamond does not conduct electricity.
Graphite is also used as stove polish and dry lubricants in the electrical industry.
The central electrode of a dry cell battery is made of carbon.
Pencil leads, 0.7 mm diameter have about 1.3 Ω resistance.
When 15V AC is impressed across the ends a current of 1A ensues and they get very hot (Joule heating).
Carbon composition resistors are made from a moulded carbon powder that has been mixed with a phenolic (or wax) binder to create
a uniform resistive body.
It is then surrounded in a insulating case after attaching end leads.
The greater the % carbon the lower the resistance.

35.41.4 "Lead pencils"
Graphite was formerly thought to be a type of lead so it was called plumbago, black lead.
This is the origin of "lead pencils", which contain no lead, and the word "plumbers" who worked with lead pipes.
Graphite is a soft, black and opaque, shiny semi-metal, greasy to touch and leaves a grey dust on the fingers,
so it is a good lubricant for machinery.
It has a hexagonal atomic structure with all atoms in the lattice strongly held in a bond with no free electrons,
which allows graphite to conduct electricity.
It was used in the first light filaments because it has a high melting point and glows white hot when
electricity passes through it.
Also, it was used to cast cannon balls.
In a "lead pencil", the "lead", or "blacklead", is graphite (plumbago) + some iron, but no lead.
When graphite is put under stress, e.g. press down on a "lead" pencil, weak van der Waals forces break,
leaving layers of graphite on the writing page to mark the paper.
The softest 9B pencil is 25% clay and 75% graphite, which changes in equal steps through HB to the
hardest 9H pencil which is 75% clay and 25% graphite.
So the softer lead pencils, the "B" grade, contain more graphite in the "lead" than the harder H grade.
Use lead pencil "lead" to unstick a zip fastener.

35.41.5 "Aquadag"
"Aquadag" (trade name) (Aqueous Deflocculated Acheson Graphite) (colloidal graphite), oildag, plumbago, "black lead",
pyrolitic graphite, black lead, stove lead, a form of graphite that occurs as mineral deposits or is made from petroleum,
used in the "lead" of soft "B" pencils, as a lubricant and electrical conductor, in cast iron and as coke for heating, in cathode ray tubes