Since diamonds are formed in earth's magma
Scientists are unsure about the exact formation conditions for
diamonds: it is possible that they crystallise in liquid magma, but
it is also possible that they crystallise in solid rock.
and pulsed to the surface through quick explosive eruptions
without changing temperature or pressure
The pressure and temperature change enormously. However, in a
kimberlitic explosive eruption, the diamonds are blasted to the
surface so rapidly that they cool down before they have time to
metamorphose into graphite.
does anyone know how a minute crystal of red (ruby? garnet?) can
become imbedded in the diamond?
The red crystal you see is probably garnet. Ruby is also a
possibility, but ruby inclusions are MUCH rarer than garnet
inclusions (years ago, it was assumed that the red crystals were
rubies but this has been shown to be incorrect in most cases).
Basically, the diamond crystallises in eclogitic or peridotitic
rock deep below the surface of the Earth. As it grows, it can
enclose small crystals of the minerals around it. These can be
various different types of garnet (usually reddish, violetish or
purplish), or peridot (greenish crystals of olivine, forsterite,
etc.). The diamond crystal is then blasted up to the surface -
possibly four billion years later.
As far as I've read, only diamonds and peridot come up from magma
So do garnets, and several other minerals.
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