For the sake of clarification, diamonds are formed just below the
earth’s crust (not in the core), and not from decomposed animal
matter, but from when tremendous heat and pressure on rocks called
eclogites (ECK-low-jites) and peridotites (per-RID-doe-tites), which
lend carbon atoms to the mix.
After diamonds (and many other gem materials) have formed from this
process, a geologic event called a magma intrusion can occur. If the
timing is right, water filtering down from the surface causes a very
rapid expansion of gases, and a type of rock called kimberlite (or
sometimes, lamproite, as in the Argyle mine’s composition), forms
along with it. As this formation occurs, the gases and rock travel
faster and faster toward the surface, bringing the diamonds, garnet,
spinel, etc. up to the surface in an ever-expanding, inverted
cone-shape that results in what is known as a kimberlite eruption.
Many of these other gem materials are found as inclusions in
diamonds.
By the time it all erupts, it is traveling at over 125 feet per
second, tossing tonsts of material into the air. When it all settles
down, this “pipe” is sometimes diamondiferous enough to develop and
mine for the diamonds. But don’t count on witnessing a kimberlite
eruption, there hasn’t been one in hundreds of thousands of years.
James in SoFl who still isn’t partial to diamonds, but certainly
doesn’t dislike them. I’d still rather have a fine opal.