A mineral is a naturally occurring homogeneous substance, which has a more or less definite chemical composition, and definite atomic structure. The minerals are usually formed by inorganic processes. They possess a set of constant physical properties. Since the determination of atomic structure and chemical composition requires complex laboratory tests, the more easily recognized physical properties are used in the identification of minerals in the field.
The minerals may be divided into two broad groups: (i) rock-forming minerals, and (ii) ore-forming minerals. Rock-forming minerals are those, which have a greate economic importance, and are found in abundance in the rocks of the earth’s crust. ”Ore forming minerals” are those, which are of economic value and which do not occur in abundance in rocks.
Minerals, being natural chemicals, are classified according to their chemistry and crystal form. A basic classification for minerals is:
- Native elements. examples; Gold, Silver, Mercury, graphite, diamond.
- Oxides. examples; corundum (incl. sapphire), hematite, spinel.
- Hydroxides. examples; Goethite, brucite.
- Sulfides. examples; Pyrite, galena, sphalerite.
- Sulfates. examples; Baryte, gypsum.
- Carbonates. examples; Calcite, magnesite, dolomite.
- Phosphates. examples; Apatite, monazite.
- Halides. examples; Fluorite, halite (rock salt).
- Silicates. examples; felspar, mica, Hornblende, Augite, Olivines etc. (it is most common mineral), it has sub-groups:
- Orthosilicates. examples; Garnet, olivine.
- Ring silicates. examples; Tourmaline, beryl.
- Chain silicates. examples; Pyroxenes, amphiboles.
- Sheet silicates. examples; Muscovite mica, biotite mica, clay minerals
- Framework silicates. examples; Quartz, feldspars, zeolites
Over 2000 minerals are known to exist but most of them are rare. The minerals which occur in common rocks are small in number. They are about 29. It is also interesting to notice that only 8 elements compose the bulk of these minerals and about 98% of the continental crust. These 8 elements are oxygen, silicon, aluminium, iron, calcium, potassium, sodium, and magnesium. Out of these two most abundant elements are silicon and oxygen, which combine to form the mineral group known as ”silicates”. The minerals which occur in common rocks can be divided into Oxides, Sulphides, Carbonates, Phosphates, Hallides, and Silicates.