Page 6 - Curriculum Visions Dynamic Book

Minerals containing aluminium
Aluminium is one of the most common elements in the rocks of the Earth’s surface, yet it is very rarely seen as the shiny metal we are used to seeing as soft drink cans etc. This is because aluminium easily combines with silicon and oxygen to make clay, the stuff of soils.
Micas
Micas are minerals made of sheets of aluminium,
silicon and oxygen (known as aluminosilicates). Stacks
of these sheets are connected together by metal ions; potassium and magnesium are among the most common.
The way the sheets are connected together is very important because it gives the minerals many of their properties. Sheet silicates all break up into thin flakes. For this reason, several of the sheet silicates are used as lubricants; for example, talcum powder is made from the mineral talc.
Mica is easily recognised as a silicate because it peels away into thin, almost transparent sheets. The main varieties are biotite, which is black, and muscovite, which is brown.
 Feldspar crystals are opaque and either pink or white. You can see them clearly in this granite sample.
Feldspar
Feldspars are
common silicate
minerals and found in
most igneous rocks. To
form an aluminium silicate
of this kind, some of the oxygen
atoms found in silica are replaced
by aluminium atoms together with a
small proportion of atoms of the metals potassium, sodium or calcium. Variety in the colour of feldspars is influenced by the proportions of these metals. For example, potassium feldspar is pale pink, whereas calcium feldspar is white.
 Muscovite, a brown form of mica.
Corundum
Corundum is a very hard, brown to black mineral, next only to diamond in its hardness. It is an aluminium oxide and is found next to where granite and other volcanic rocks occur. The
material we call emery is made from corundum. Emery cloth is
a common abrasive cloth, while emery powder is glued on to discs to make cutting and sanding tools.
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