Coal is basically a compound consisting largely of carbon. When a piece of carbon deep under-ground is subjected to great heat and pressure, it may gradually be transformed into a diamond. The heat turns the carbon into a liquid and the pressure causes it to crystallize.
Thus the carbon loses its black unattractive appearance and becomes the most precious of stones.
It has been calculated that this extraordinary process takes place at least 75 miles beneath the earth’s surface, the diamonds being afterwards transporated upwards by natural forces.
Some iron meteorites full of carbon have been found to contain diamonds deep inside. Here the heat and pressure conditions would once have been much the same as those formed underground.
Much the same conditions are created in the laboratory to make synthetic diamonds for industrial purposes, such as cutting hard materials. Only industrial diamonds are man-made. The diamonds that are considered the most precious stones in the world took thousands of years to form.
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