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Excerpt from section 2 of the exhibition
FROM THE DEPTHS OF THE EARTH
WHERE DO DIAMONDS FORM?
The ultrahigh pressure under which carbon atoms are “squeezed” into diamond is difficult to imagine. For example, the pressure of 55,000 atmospheres necessary to make a diamond at 1400 ºC would require 7,000 metric tons, the same weight as the Eiffel Tower, resting on a 12.5-cm plate.
Such pressures are found in nature. But to find them, one must penetrate the Earth’s surface and go down, down, down... more than 150 kilometres down, to a layer beneath the crust known as the mantle
Credit: American Museum of Natural History
Crystallized deep within the Earth, diamonds are sometimes captured by rising magma, burning lava that spurts out violently and eventually cools down in the volcano chimney, forming a pipe that might one day be exploited as a diamond mine.
Only two types of magma are diamond bearing, that is, likely to contain diamonds. The most abundant is called « kimberlite ,» after Kimberly, a small town in South Africa where such chimneys were first discovered in the 1870s. The other type is called lamproite.
A Tremendous Pssssst!
The magma rises slowly in the depths of the Earth and then more and more swiftly as the ambient pressure decreases… until, nearing the surface, the gases dissolved in the liquified rocks suddenly turn into bubbles, making the lava erupt extremely violently at a supersonic speed!
This type of volcano is very small compared with gigantic Mount St. Helens, for example. However, its magma originates at at least three times the depth in fissures or dykes so deep within the mantle that the rocks in which diamonds have crystallized are stripped off as the magma rises.
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