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 Diamond Geology |
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 Formation in the earth |
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| Diamond is a
polymorph form of carbon. The other form is graphite. For carbon to turn into diamond,
3 factors are needed: time, very high temperature (around
1,000 degrees) and very high pressure above
30 kilobars (kb). The Pressure and Temperature conditions within the earth, are known as
geotherms. Any changes of « P » (Pressure) and « T » (Temperature) within the environment where
diamonds are formed, may reverse the cycle back to graphite or gas. The main bearing diamond rocks are
kimberlite (the name proposed by Lewis in 1888 is for the Kimberley district in South Africa), eclogite,
lamproite. Diamonds can be formed going down towards the mantle of the earth (subduction), going up
towards the surface of the earth (obduction) and also on impact (meteorites). |
| The most common shape of kimberlite pipe is
« the carrot shape » it also occur as dykes and rarely as sills. Within the kimberlite
pipe 3 zones are recognized, the crater, diatreme and the root zones. The pipes do vary
in size, up to 200 hectares. In contrast to kimberlites, which may show some vertical flaring over 1 to 2 kms,
Lamproite bodies are shallower, around 0.5 kms in depth . Many lamproites
have a champagne glass shape craters. The difference between kimberlites and lamproites pipe shapes has
important implications for exploration (ore volume calculations). |
| Click here to see a multimedia presentation of are diamonds transported
to the Earth's surface. You will need to have the Real Player installed to
view this movie. If you do not have it, you can download a free version of
the Real Player. |
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| Diamonds found in meteorites |
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| Diamonds in meteorites were discovered in Arizona or
South Pole and they contained minuscule crystals of diamonds. In 2004, The Harvard-Smithsonian Center for
Astrophysics has announced the discovery of a mass of crystallized carbon formerly known as star BPM 37093,
now known as the biggest diamond in the galaxy, fifty light years away from Earth in the constellation
Centaurus. The diamond is estimated to be 2,500 miles across and weighs approximately 10
billion-trillion-trillion carats – a one, followed by 34 zeros = 10,000,000,000,000,000,000,000,000,000,000,000
carats. For more informations, click: 10 Billion-Trillion-Trillion-Carat Diamond Found in Space |
| Types of diamond deposits |
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| Primary deposits |
Secondary deposits |
 Diamantiferous kimberlite lamproite pipes
are the « Primary deposits ». Diamonds are transported to the surface of the earth by the magma pushing upwards
the kimberlite (diamond bearing rock ) at great velocity. When it reaches the surface, the volcanic eruption
occurs releasing an enormous energy creating the birth of the volcano. The material blown out from the
explosion probably landed in a pile around the vent. The material eventually washes away by rain or washes
back into the central zone of the crater or is dispersed by other weathering processes. The kimberlite that
remain in the cracks of the earth crust crystallize as dykes. |
The secondary deposits are formed by the
weathering of the kimberlite and the lamproite. The diamonds are released from the rock and then, they are
transported hundreds of kilometres away to be found in river beds, beach sands, old river beds (sometime
found on top of hills deep jungle forest, deserts, etc... Diamonds may also have been transported by
glaciers and if the journey has been hard, rough and long, they are not to be found as they have been broken
and grinded into near dust. |
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| World wide diamondiferous deposits |
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) Click to enlarge |
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