Minerals

Minerals are naturally occurring substances having a definite chemical composition. They are grouped into classes, generally as rocks, non-metallic, mineral fuels and metals.

OCCURRENCE

Metallic minerals, such as copper, tin, lead and zinc may occur in almost pure form in veins-a fissure in rock strata containing a thin deposit of crystalline rock formed by extremely hot solutions rising from magma-and lodes (very thick veins). An ore is a deposit from which a mineral is obtained. In some ores, several metals are associated together---e.g., silver and mercury are associated with lead and zinc. Some minerals occur in beds or layers which have formed due to deposition, accumulation and concentration in horizontal strata of the earth's 'crust. Examples are coal and some grades of iron ore. They are concentrated as a result of long periods under great heat and pressure.

Minerals like gypsum, potash salts and common salt are formed by the evaporation of lakes in desert areas. Bauxite is formed by the deep-weathering of a variety of rocks under tropical conditions with a climate of seasonal rainfall. Minerals like gold, tin and platinum are highly resistant to weathering, and may get removed in small particles from veins by erosion and carried off by running water in streams and rivers to be deposited in the plains or valleys below. These are known as alluvial deposits. Tin, gold, platinum, chromite, tungsten, diamonds and zircon are recovered from alluvial deposits by placer mining methods.

Minerals are distributed very unevenly over the earth's surface. In some places, e.g., in the Urals of Russia, in theCanadian Shield, the Katanga in Zaire, and in South Africa, a variety of minerals occur in great abundance:- M: the Amazon basin, the Netherlands, Denmark and some of the Central American states are poor in minerals.

Some min­erals are found in restricted areas of the world: tin, vanadium, nickel, cobalt, gold and asbestos are examples of such minerals. More than 50 per cent of the world's tin comes from eastern Asia (Malaysia, Thailand, China, Indo­nesia); the USA is the largest producer of some minerals such as molybdenum, sulphur and phosphates; Canada dominates in nickel production. Many of the more valuable minerals, including gold, are found chiefly in Africa, with South Africa accounting for nearly 70 per cent of the total. Africa also holds valuable deposits of cobalt, diamond and platinum.