Geography

Mode Of Occurence Of Minerals
1. Minerals in igneous and metamorphic rock :
The minerals are found in crevices, faults or joints. The smaller occurence are called veins and larger lodes. In most cases, they are formed when minerals in liquid/molten/gaseous form are force upwards through cavities towards the earth’s surface. They cool and solidifies as they rise. Major metallic minerals like Tin, copper, Zinc and Lead etc are obtained from veins and lodes.
2. Minerals in decomposed rocks :
This involves the decomposition of surface rocks, and the removal of soluble constituents, leaving a residual mass of weathered material containing ores, Bauxite is formed this way.
3. Minerals in alluvial deposits :
Certain minerals may occur as alluvial deposits in sands of valley floors and the base of hills. These deposits are called “Placer deposits” and generally contain minerals which are not corroded by water. e.g. Gold, Silver Tin etc.
4. Minerals in sedimentary rocks :
In sedimentary rocks a number of minerals occur in beds or layers. They have been formed as a result of deposition, accumulation and concentration is horizontal stratas coal and some forms of Iron ore have been concentrated as a result of long periods under great heat and pressure. Gypsum, salt, Potash and Sodium salt are formed as a result of evaporation especially in arid regions.
5. Minerals is ocean water :
The minerals which are found in ocean water are called ocean water minerals e.g. common salt, Magnesium and Bromine are largely derived from ocean water.
6. Minerals are very unevenly distributed :
1. Minerals in Deccan : The peninsular rock contain most of the reserves of coal, metallic minerals, mica and many other non-metallic minerals.
2. Minerals in western and eastern region of India : Sedimentary rocks of the western and eastern parts of India. i.e., Gujarat and Assam have most of the petroleum deposits.
3. Minerals in Rajasthan : Rajasthan with the rock system of the peninsula, has reserves of many non-ferrous minerals.
4. Minerals in North India : North India is almost devoid of economic minerals.
Concentration of minerals in the ore, the ease of extraction and closeness to the market play an important role in affecting the economic viabiliity of a reserve.