Diamond
The name Diamond comes from the Greek word 'Adamas' the unconquerable, in recognition of the hardest naturally occurring material. In ancient times it would have been impossible to fashion them because of their hardness; they could only be set as point stones; octahedral crystals in their natural form..
There are many famous diamonds, some with a long and unclear history. The largest cut diamond is the Cullinan 1, a pear-cut stone at 530.20 carats, named after Sir Thomas Cullinan, chairman of the Premier mine near Johannesburg. It was set into the British Royal Septre and remains on display in the Tower of London.
Traditional diamond cutting is a long job, the process involves cleaving - slicing off sections, Bruting - basic girdle shaping by using another diamond as a lathe tool. Then cutting and polishing - using laps charged with differently graded diamond grit. Large diamond cutting firms with modern facilities, use lasers to cut diamonds; greatly increasing production. More valuable stones are still cut by traditional methods.
The most popular cut for diamond is the brilliant cut, of which several variations exist. The angles of facets on the pavilion and crown and the size of the table are important factors when designing a stone. The size of the table facet determines the amount of brilliance and dispersion (fire) that the stone returns. A larger table facet increases brilliance and reduces dispersion and a smaller table has the opposite effect. Fire refers to the spectral colours that are seen through the crown facets. The pavilion facet angles are critical and provide Total Internal Reflection (TIR) of light, necessary for maximum brilliance.
There are now many fancy coloured diamonds on the market due to irradiation treatments, natural blue diamonds are very rare but readily available as enhanced stones.
Accent diamonds are small stones, commonly used to compliment other precious and semi-precious gemstones.
Diamonds are often associated with the familiar four C's grading system: Colour, Clarity, Cut & Carat weight. There are different grading systems in use, employing many parameters to derive at the correct value of the diamond.
Major source locations for diamond include: Africa, Australia, Canada, China and Russia.
Properties of the Gemstone and Additional Information
| Gemstone type: | Diamond |
| Crystal System: | Cubic (isometric) |
| Chemical Composition: | Carbon, C |
| Colour: | Colourless, off-white to yellow, pink, brown, black, rarely as green, blue, red or purple |
| Lustre: | Adamantine: the highest lustre |
| Pleochroism: | None |
| Dispersion: | High at 0.044 |
| Hardness: | 10 on the Mohs' scale, the highest of all gemstones and all known naturally occurring substances. |
| Toughness: | Good |
| Cleavage: | Perfect: cleaves to produce totally flat planes. |
| Density in gm/cc: | 3.52 |
| Double refraction: | None |
| Refractive index: | 2.42 |
Common Treatments
Irradiation and heat treatments are used to clarify or colour stones.
Laser Drilling is used to remove black inclusions, the cavity is usually filled with glass. Natural cavities and surface depressions are also glass-filled.
High tech coatings have been applied to colour diamonds.
HPHT (high pressure high temperature) treatment is used to remove the brown colour from some diamonds by straightening a 'twisted lattice', the cause of the undesirable colour.
Diamonds may be manufactured using a HPHT method that employs seed diamonds and carbon material. They sell at a much lower price than natural diamonds.