Glossary

Abrasive

A material used for grinding or polishing.

Abundant

Present in great quantity.

Alloy

A mixture of two or more metals, or a metal and a non-metal. For example, brass is an alloy of copper and zinc, and steel is an alloy of iron and carbon.

Alluvial

Sediment deposited by a stream or river.

Aluminium

A light, ductile and malleable silver-white metal. The chemical symbol for aluminium is Al.

Argentite

A silver sulphide mineral, the main ore for silver. The chemical formula for argentite is Ag2S.

Atomic mass

The mass of one atom of an element

Azurite

A blue mineral containing copper. It is composed of copper carbonate - chemical formula Cu3(CO3)3. It has a hardness of 3.5-4 and produces a blue streak when scratched on a white tile.

Basalt

A dark igneous rock. Basalt originates from lava that has extruded onto the surface of the Earth. Therefore the lava has cooled quickly, forming small crystals.

Carat

A unit of weight for diamonds, pearls and other gemstones. 1 carat = 200mg. or;

A unit used to measure the purity of gold. i.e.

Cerargyrite

Silver chloride; with the chemical formula AgCl, an important silver ore; also called horn silver.

Chalcopyrite

A mineral containing copper. Its chemical name is copper iron sulphide - chemical formula CuFeS2. It is brassy yellow in colour, has a hardness of 3.5-4 and produces a green streak when scratched on a white tile.

Compound

A combination of two or more different atoms bonded together. For example common table salt is a compound of the elements sodium and chlorine.

Conduct

To transmit or serve as a channel or medium for heat, electricity or sound.

Conductivity

The power of conducting heat, electricity or sound. Thermal conductivity is the power to conduct heat; electrical conductivity is the power to conduct electricity. Silver, for example is an excellent thermal and electrical conductor. It transmits both heat and electricity very well.

Copper

A fairly soft metal (hardness 2.5-3.0.) It is an excellent conductor of heat and electricity, and is very malleable and ductile. It has a characteristic red colour when fresh (copper-red), but tarnishes to a greenish colour (have a look at an old 1 or 2 cent coin). Copper dissolves easily in acid. Because it is such a good conductor and it is so ductile, copper is mainly used in electrical goods. The chemical symbol for copper is Cu.

Copper sulphate

A compound of copper and sulphur, blue in colour. The chemical formula for copper sulphate is CuSO4.

Corrode

To eat away the surface of a solid (especially metal), by chemical action.

Corrosion

The act or process of corroding.

Density

The density of a substance depends on both its mass and its volume.

For example, feathers are less dense than lead. 1 tonne of feathers will have a greater volume than 1 tonne of lead. Similarly, 1 litre of lead will have a much greater mass than 1 litre of feathers.

Density can be calculated by the equation: density =  mass
volume

1 litre of water has a mass of 1 kilogram, therefore the density of water is 1. Gold has a density of 19.3.

Ductile

Describes a substance that can be stretched or drawn out into thin wire. Gold and copper are very ductile.

Element

A substance which cannot be split into simpler substances by a chemical reaction. An element is a substance that consists of the same type of atoms. For example the element oxygen contains only oxygen atoms, whereas the compound water contains atoms of the elements oxygen and hydrogen bonded together.

Freibergite

A silver mineral with the chemical formula (Ag,Cu)12(SbAs)4S13.

Galena

A soft, heavy bluish-grey mineral, chemical formula PbS (lead sulphide). Galena is the most important ore of lead and one of the most important sources of silver.

Goethite

A yellowish, reddish, or brownish-black mineral, with the chemical formula FeO(OH). Goethite commonly forms as a weathering product of iron ore.

Gold

A heavy, soft, yellow, chemically stable metal. Gold has a hardness of 2.5-3, and is very malleable and ductile. The chemical symbol for gold is Au.

Gold pan and cradle

Tools used by gold diggers to separate gold from dirt.

Granite

A coarse grained igneous rock containing the minerals mica, quartz and feldspar. Granite forms from the solidification of magma deep below the Earth's surface. The magma cools very slowly, allowing big crystals to be formed.

Hematite

A common iron mineral with the chemical formula Fe2O3.

Igneous rock

Rocks formed from magma that has cooled and solidified either at the Earth's surface (eg basalt) or deep below the Earth's surface (eg granite).

Iron

A metal which is mainly used to make steel. Pure iron rusts quite easily, forming iron oxide. Pure iron is quite soft, but can be made much harder and stronger, by adding a small amount of carbon to it when it is molten. The chemical symbol for iron is Fe.

Lead

A heavy (density 11.3) soft metal, with a dull blue-grey appearance. It has a low melting point, and for this reason it has been used in solders. Lead is a toxic substance. Its main use is in batteries; especially those used in vehicles. Its chemical symbol is Pb.

Limonite

A dark brown or yellowish-brown mineral with the chemical formula 2Fe2O3. 3H2O. Limonite is commonly formed by the oxidation of iron minerals.

Magnetite

A black, magnetic iron mineral with the chemical formula (Fe,Mg)Fe2O4.

Malachite

A green mineral containing copper. It is composed of copper carbonate (chemical formula Cu3(CO3)2. Malachite is a weathering product of azurite, which is a blue copper carbonate mineral.

Malleable

Describes a substance that can be shaped by hammering or by pressure from rollers.

Mercury

The only metal which is a liquid at room temperature. It takes the form of tiny silver drops. It is very heavy and is an excellent conductor of heat and electricity. Mercury easily forms an alloy with gold (known as an "amalgam"). For this reason it was commonly used by the gold diggers to extract gold from crushed rocks and river sediments. The chemical symbol for mercury is Hg, and it has a density of 13.6.

Metamorphic Rock

A rock that has changed after being subjected to heat and/or pressure. For example limestone is a sedimentary rock which, if subjected to heat and/or pressure, changes to the metamorphic rock called marble. Slate is a metamorphic rock derived from shale.

Meteorite

A mass of stone or metal that has reached the Earth's surface from outer space.

Mineral

A naturally occurring substance which has a definite chemical composition and crystal structure.

Mohs Scale

A standard hardness scale, called Mohs Scale of Hardness, is named after the scientist Friedrich Mohs. This is simply a scale from 1 to 10, where 1 is the softest and 10 is hardest. (eg, quartz with a hardness of 7 will scratch orthoclase, which has a hardness of 6, diamond (hardness 10) will scratch everything). We can compare the hardness of common substances with the minerals in Mohs Scale of Hardness:

Diagram of Mohs Scale of Hardness

Pegmatite

A light coloured igneous rock containing large crystals of the minerals mica, quartz and feldspar.

Precipitate

A solid which sometimes forms as a result of a chemical reaction when two solutions are mixed. The solid formed is insoluble (won't dissolve) in the solution

Proustite

A red mineral with the chemical formula Ag3AsS3. Proustite is a minor silver ore.

Pyrargyrite

A dark red, grey or black mineral with the chemical formula Ag3SbS3. Pyrargyrite is an important silver ore.

Quartz

A very common rock-forming mineral. It consists of silicon dioxide (silica), and has a hardness of 7.

Relative Density

The mass of a volume of a substance, relative to the mass of the same volume of water. Another name for Relative Density is Specific Gravity. 1 cubic centimetre (cc) of water weighs 1 gram. The Relative Density of water is 1. 1cc of gold weighs 19.3 grams. Its Relative Density is 19.3.

Sedimentary

rocks formed by the deposition of sediments. For example sandstone, limestone and shale.

Silica

Silicon dioxide, SiO2.

Silver

A fairly soft (2.5-3), very heavy (density 10.5), ductile and malleable metal. It is the best known conductor of heat and electricity. Silver is mainly used in photographic paper and film, followed by the electronics and jewellery/tableware industries. The chemical symbol for silver is Ag.

Solution

When substances are dissolved in a liquid, the resulting mixture is called a solution.

Streak

The colour that a powered mineral leaves when it is scratched on an unglazed white tile. Scientists use the streak of a mineral as an identification method. Even with the presence of impurities, the colour of the streak remains constant.

Pyrite (fool's gold) is a mineral which has a streak colour (black) very different from the colour of the mineral itself. This is very handy for determining whether a sample is real gold or fool's gold. Pyrite will leave a black powder if it is scratched on a white tile, whereas real gold will leave a yellow/gold smear.

Tetrahedrite

a steel-grey to iron-black mineral with the chemical formula (CuFe)12Sb4S13. Often tetrahedrite has silver replacing the copper, so the chemical formula becomes (AgFe)12Sb4S13.

Tin

A metal with a low melting point; therefore it is often used for solder. It is malleable and resists corrosion. Tin is used to produce tinplate (steel coated with tin) for food packaging. The chemical symbol for tin is Sn and it has a density of 7.3.

Troy ounce

A unit for measuring the weight of gold. One troy ounce of gold weighs approximately 31.1 grams. The word "troy" is named after the French town of Troyes.

UV

Ultraviolet light.

Weathering

The destructive effects of air, wind, water or ice, by which rocks are changed in colour, texture, composition or form. Most weathering occurs at the surface, but it may take place deep under the surface as water and oxygen penetrates into rocks through joints.

Zinc

A blue-grey metal used for galvanising (coating) iron and steel to protect against rust. The main zinc mineral is sphalerite. Brass is an alloy of copper and zinc. The chemical symbol for zinc is Zn.

Minerals Downunder