Q21 of 141 Page 455

How do minerals occur in (a) igneous and metamorphic rocks? (b) in sedimentary rocks?

a. Igneous rocks and Metamorphic rocks: The minerals in these rocks exist in the cracks, crevices, faults or joints. When minerals are found in small amount is called veins and lodes when found in large amount.


When minerals are in liquid or molten or gaseous form, they are forced towards the earth surface. Then they cool and solidify as they rise. Minerals like copper, zinc are obtained from these rocks.


b. Sedimentary: The minerals in these rocks are found in beds or layers.


Coal and some other forms of iron ore have been concentrated for long periods under high pressure and heat. This deposition and accumulation and concentration in horizontal strata form these rocks.


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