Explain why most Quartz is not considered a gems stone.while amethyst which is a kind of quartz is a gems ston?
it doesn't when it reaches the surface, it become ultramafic rock, such as peridotite, pyroxinite and dunite (among many others) The granite was formed billions of years ago, when the least dense rock in the young earth rose to the surface forming the continental crust sometimes ultramafic rock, may mix with granitic rock, forming an intermediate or mafic rock that contains some quartz. But mantle rock itself never becomes granite
Granitic magmas could be derived from partial melting of basaltic rocks, yet maximum are derived from melting of older granitic rocks or sediments that have been deeply buried or are dragged down into subduction zones. they might additionally be formed by using fractional crystallisation of intermediate or undemanding lavas - the granite magma could be the final area of the soften to crystallise and if the crystals are bumped off the effect is a granite.
