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The Creation of a Diamond

Diamonds are formed deep beneath the Earth's surface; between 100 and 200km below. They are formed by remarkable conditions which make diamonds so rare.

In this part of the Earth's mantle temperatures are from 900 - 1300C, with pressures of 45 - 60 kilo bars.

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 volcanic rock known as kimberlite. 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). 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. Within the last few kilometers, the eruption velocity probably increases to several hundred km/hr.

All natural diamonds are at least 990,000,000 years old. Many are 3,200,000,000 years old (3.2 billion years). This can't be determined by Carbon Dating as this technology only works for very young carbon. Scientists use other radioactive decay schemes (e.g., uranium-lead) to date inclusions in diamonds. Inclusions used for dating are around 100 microns in diameter.

Volcano Eruption

Diamonds: The Hardest Material.

Diamond is the hardest gem on the Mohs hardness scale and graphite (also made from carbon atoms) is the softest! The rating of a mineral's "hardness" or resistance to being scratched can be given using Mohs' scale. This was devised by the German geologist Frierich Mohs (1773-1839).

Rating Type mineral Everyday equivalent
1 Talc Baby powder
2 Gypsum fingernail
3 Calcite bronze coin
4 Fluorite iron nail
5 Apatite glass
6 Feldspar penknife blader
7 Quartz steel knife
8 Topaz sandpaper
9 Corundum  
10 Diamond  

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).

How rare are diamonds? How many grams do you need to mine to get 5 grams of diamonds?

Only 5gm in every 1000kg of mined material is diamond. Of this, only 20% are of gem quality, of which even fewer are of the high quality we sell at Jason Withers Original Diamonds. The remainder are used for industrial purposes.

Basic Data Hardness = 10
Crystal System = cubic
Refractive Index = 2.42
Dispersion = 0.044
Specific Gravity = 3.52

Laser inscribed diamond

Treatments & Synthetics

Surface cracks, fractures and cleavages reaching the surface can be filled with a glass-like material with similar RI (refractive index; the degree to which incident light is bent upon entering the stone). However when examined with an optical microscope, filled stones will show a greasy appearance, flash effects and bubbles.

The problem with filling is that it does not always resist polishing, heating, cleaning and age wear. Filling of inclusions involves using a laser to drill into the diamond. Solutions can be poured into the resulting hole to bleach coloured inclusions, but again is not as resistant as natural diamond.

Synthetic diamond Fracture filled diamond

Irradiation is used to change the colour of the diamond. A common colour produced by irradiation are greens yellow and blues, usually very intense and unnatural looking.

Laser drilled diamond to remove inclusions

Synthetic diamonds are often yellowish in colour and are rarely used for high-quality jewellery. They are more commonly used as diamond grit for industrial purposes. A 5mm diamond (0.5 carat) takes over a week to grow. Synthesis requires:

  • High pressure
  • High temperature
  • Special apparatus

Synthetic diamonds can sometimes be distinguished from natural diamonds by the presence metallic flux inclusions and distinctive zoning and growth patterns. Testing with advanced instrumentation provides evidence of their laboratory origin. It is illegal under Australian Federal Law to sell a diamond simulant as a real diamond.