@ syeda sabahat....
hmmmm... thanks sister....
@ erum qureshi....
yes syeda sis is saying right this question belongs to geology and i have studied geology in my engineering course... the type of minerals found in the earth are the result of different conditions prevailing. if a mineral is at low depth then overburden (the material above it) is less and the pressure is less also the weight so they can be easily extracted or exploited (digged) and if the pressure increses owing to the increse in wieght then they get hard and u have to employ different method of mining them....
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