Answer 1:
Yes - different minerals form at different
temperatures and pressures. The process by which
this happens in the Earth is called metamorphism,
and rocks whose minerals have been altered by heat
and pressure in this way are called metamorphic
rocks. For example, shale is made out of quartz
and clay minerals (e.g. kaolinite). If you
metamorphose it, it turns into slate, then
phyllite, and finally schist, and what is
happening to cause this transition is that the
clay minerals are turning into micas (mainly
muscovite). If you continue to metamorphose it
will become agneiss, in which the muscovite mica
will become chlorite and then biotite. Eventually,
you melt the rock, and when you crystallize that
out, what had been clay is now a mix of biotite,
hornblende, and variousfeldspars. |
Answer 2:
Rocks are made up of minerals. In general, the
deeper one goes in earth the higher the density of
the rock and hence the minerals making up the rock
tend to be denser. So graphite is the stable
form of element Carbon at the surface but at
depths > about 150 km, diamond is the stable form
of carbon.
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