Question

Write a short note on the different modes of occurrence of minerals explain with example

Answer 1

Mode of occurrence of minerals:

1)In igneous and metamorphic rocks: The smaller occurrences are called veins and the larger occurrences 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. Examples: tin, copper, zinc, lead, etc.
2) In sedimentary rocks: In these rocks, minerals occur in beds or layers. Coal, iron ore, gypsum, potash salt and sodium salt are the minerals found in sedimentary rocks.
3)By decomposition of surface rocks: Decomposition of surface rocks and removal of soluble constituents leaves a residual mass of weathered material which contains ores. Bauxite is formed in this way.
4) As alluvial deposits: These minerals are found in sands of valley floors and the base of hills. These deposits are called placer deposits. They generally contain those minerals which are not corroded by water. Examples; gold, silver, tin, platinum, etc.
5)In ocean water: Most of the minerals in ocean water are too widely diffused to be of economic importance. But common salt, magnesium and bromine are mainly derived from ocean waters.

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Answer 2

Answer:

Minerals occur in the earth’s crust as:

Veins and lodes in igneous and metamorphic rocks

Beds or layers in sedimentary rocks

Alluvial or placer deposits on valley floors

Residual mass after weathering of surrounding rocks

Some metallic minerals, like gold, silver, platinum and tin, are found as alluvial deposits in the sand and soil in valleys. Such alluvial deposits are also called placer deposits. Around 70% of the surface of the earth is covered by water. The water of the seas and oceans, and the ocean floors, also have rich mineral deposits.

Explanation:

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