Mode of Occurrence of Minerals


 
 
Concept Explanation
 

Mode of Occurrence of Minerals

Mode of Occurrence of Minerals: Minerals are usually found in ores. An ore is a naturally occurring material having one or more minerals in sufficient concentration mixed with other elements. Mineral generally occur in these forms

  • ·Veins and Lodes: In igneous and metamorphic rocks, minerals occur in cracks, crevices, faults or joints. The smaller occurrences are called veins and the larger are called lodes. They are usually formed when minerals in liquid/molten and gaseous forms are forced upwards through cavities towards the Earth’s surface. They cool and solidify as they rise. Major metallic minerals like tin, copper, zinc and lead are obtained from veins and lodes.
  • Beds and Layers: In sedimentary rocks, minerals occur in the form of beds and layers. They have been formed as a result of deposition, accumulation and concentration in horizontal layers of the rock. Coal and some forms of iron ore have been concentrated here due to great heat and pressure, for long periods.  Other minerals like gypsum, potash salt and sodium salts are also found in sedimentary rocks. They have been formed as a result of evaporation especially in arid regions.
  • Decomposition of Surface Rocks: If decomposition of surface rocks occurs with the removal of soluble constituents, the residual mass of weathered material left behind contains mineral ores. Bauxite is formed in this way.
  •  Alluvial Deposits: Some minerals are found in sands of valley floors and at the base of hills. These are known as placer deposits. These placer deposits consist of minerals which are not corroded by water e.g. gold, silver, Platinum and tin.
  • Ocean Waters: These contain many minerals. Common salt, magnesium and bromine are derived from ocean waters, whereas manganese nodules occur in ocean beds.
  • Sample Questions
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    Question : 1

    Minerals are deposited and accumulated in the strata of which of the following rocks?

    Right Option : C
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    Question : 2

    A period of the Earth's geological history which ia about 55 million years old was ______ .

    Right Option : C
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    Question : 3

    A period of the Earth's geological history which is about 55 million years old was ________________________

    Right Option : C
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