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About150 to 300 kilometres under the
earth's surface, are small amounts of black carbon. Around
2.5 billion years ago the heat and pressure was strong
enough to turn the carbon into diamond. Then a very small
part of the newly formed diamonds were, quite luckily,
pushed upward near the earth's surface through volcanic
eruption. The forming of carbon, and its changing into
diamond could take hundreds of years. The 300 kilometre
journey to the surface of the earth happened in a matter of
hours during an eruption. Then millions of years passed
before the diamonds were found or mined. The last known occasion in which
diamonds came to the surface was about 40 million years ago
in E. Africa. The youngest diamonds known are 1 million
years old and many are over 3 million years old. It is
unknown how much carbon has been turned to Diamond deep down
in the center of the earth but its pretty certain that a
very small percent of it was lucky enough to be brought up
by a volcanic eruption. The small amount that is brought up
is in little pieces, and each piece has approximately 5 tons
of dirt & rock around it. All volcanic eruption do not
necessarily bring up diamonds, as only 1 % of all the
volcanic eruptions are actually found to be economical for
producing diamonds.