|In what form are metals found?|
Metals rarely occur in nature in their pure metallic state. Only gold, silver and copper (so-called native silver and copper) have been found as metals. All of the other metals occur in nature as compounds combined in structures called minerals. Rocks are composites of different minerals formed through the cooling of liquid magma, altered by the action of wind, water, glaciers and gravity, or changed through the effects of pressure and temperature as the earth evolved. There are about 3 000 known minerals, each with its own fixed chemical formula, the large majority of which contain metals.
The main categories of minerals are:
Oxides, which are the source of aluminum (bauxite), iron (magnetite and hematite), tin (cassiterite), chromium (chromite), manganese (pyrolusite), nickel (laterite) and uranium (uraninite).
Carbonates of sodium, calcium (limestone) and magnesium (magnesite).
Sulphides, which host metals such as copper (chalcopyrite), zinc (sphalerite), nickel (pentlandite), lead (galena), mercury (cinnabar) and iron (pyrite).
Sulphates, such as that of calcium (gypsum).
Phosphates, in which vanadium is found.
Silicates (silicon oxides) of zirconium and aluminum.
Halides (compounds with chlorine, fluorine, bromine and iodine) of sodium (sodium chloride is common table salt) and potassium.
It is from this host of naturally occurring minerals that the mining industry derives the large bulk of structural and functional materials.