Magnesium does not occur free in nature. It is the lightest metal known and is found in a large number of minerals. The magnesium minerals of economic importance are:
Among the above minerals, magnesite is the only important ore-mineral of magnesium. There are two main varieties of natural magnesite (i) crystalline or spathic and (ii) amorphous (cryptocrystalline) or massive. In general the amorphous variety, though less common in occurrence is purer than the crystalline variety.
1. By residual concentration.
2. It is generally believed as Sir Thomas Holland puts it that magnesite was formed by the action of superheated C02 and H20 which were derived from magma. The superheated C02 and H20 acted on the peridotite, dunite and serpentine converting the magnesium silicate to magaesite. It is also believed that Si02 which gets liberated occurs as chalcedony or quartz within magnesite.
H4Mg3Si09 +H20+C02àMgC03 + Si02+H20
Mode of occurrence:
Magnesite occurs as irregular veins and fracture zones in serpentine masses.
Distribution in India:
In India, the principal magnesite deposits are found in Tamil Nadu (chalk hills and adjacent areas in Salem district and in Tiruchirapalli district). The other occurrences are
Dodkanya and Dodkatur areas in Mysore and Hassan district.
(b) Uttar Pradesh:
Someshwar and Bageshwar areas in Almora district.
(i) Powder for flash lights, photography and fire works.
(ii) Alloys used in air planes.
(iii) Metal as deoxidiser and desulphurizer of Ni.
(iv)As refractory material, like furnace lining etc.