Wednesday, April 29, 2009

Remarkable Facts of Diamonds

All diamonds are at least 990,000,000 years old.

Many are 3,200,000,000 years old (3.2 billion years)!!!
How do we know this?
Age: from Carbon dating? NO! C-dating only works for very young carbon. You need to use other radioactive decay schemes (e.g., uranium-lead) to date inclusions in diamonds. Inclusions used for dating are around 100 microns in diameter (0.1 mm).

Diamonds are formed deep within the Earth: between 100 km and 200 km below the surface.

Diamonds form under remarkable conditions!
  • The temperatures are about 900 - 1300 C in the part of the Earth's mantle where diamonds form.
  • The pressure is between 45 - 60 kilobars. (kB)
  • + 50 kB = 150 km = 90 miles below the surface
  • + 60 kB = 200 km = 120 miles below the surface
Diamonds are carried to the surface by volcanic eruptions.

  • The volcanic magma conduit is known as a kimberlite pipe or diamond pipe.

    We find diamonds as inclusions in the (rather ordinary looking) volcanic rock known as kimberlite.

  • NOTE: The kimberlite magmas that carry diamonds to the surface are often much younger than the diamonds they transport (the kimberlite magma simply acts as a conveyer belt!).

* Diamond is made of carbon (C), yet the stable form (polymorph) of carbon at the Earth's surface is graphite.

* To ensure they are not converted to graphite, diamonds must be transported extremely rapidly to the Earth's surface.

  • It is probable that kimberlite lavas carrying diamonds erupt at between 10 and 30 km/hour (Eggler, 1989). Within the last few kilometers, the eruption velocity probably increases to several hundred km/hr.

Diamond is the hardest material.

  • Diamond is the hardest gem on the MOHS harness scale and graphite (also made from carbon atoms) is the softest! Given that both diamond and graphite are made of carbon, this may seem surprising.

  • The explanation is found in the fact that in diamond the carbon atoms are linked together into a three-dimensional network whereas in graphite, the carbon atoms are linked into sheets with very little to hold the sheets together (thus the sheets slide past each other easily, making a very soft material).

* Diamonds are found in many localities, both overseas and in the US.

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