What is Diamond?

The causes of these colours lies at atomic level. Diamond comprises covalently bonded carbon atoms. In pure diamond visible light does not possess enough energy to excite electrons in the bonds and consequently no light is absorbed in the visible band and all the light falling on the diamond is transmitted and refracted back to the eye causing the diamond to appear completely colourless.

However, most diamonds are not perfect. The diamond lattice contains impurities such as nitrogen and the lattice is sometimes defective with a missing atom. This presence of impurities, or more specifically the electrons associated with the impurities, is the cause of colour in the majority of diamonds.

Yellow: Nitrogen is the cause of colour in these diamonds.
Brown: Plastic deformation of the diamond lattice whilst in the earth.
Pink & Mauve: Plastic deformation of the diamond lattice in the upper mantle region of the earth.
Black: Caused by a vast quantity of dark opaque inclusions.
Blue: Boron impurity in the lattice.
Green: Caused by alpha particle radiation.

The rarety and subsequent high value of fancy coloured diamonds has led to the development of artificial colouration of diamonds.
There are two main types:

1 Surface coating to disguise real colour of diamond
This is done by coating the diamond surface with a metal halide in a process similar to that used in producing the rich blue bloom seen on camera lenses. It is easily removed by boiling in acid for a couple of minutes, and is attacked when a working jeweller places a hot diamond in acid as part of the process of sizing a ring for example.
A light enamelling is sometimes applied to the lower pavilion facets to simulate or improve a colour.

2 Alter the body colour

Cyclotron Treatment:
This is a device used to accelerate sub atomic particles such as protons, deuterons (heavy hydrogen), and alpha particles (Helium nucleus mass 4, charge +2e) and smash them into the diamond lattice. The colour produced is from dark green to almost black. The particles are charged and depth penetration is poor, forming a skin. The colour is permanent unless the stone is repolished.
Further heating converts the green to yellow, orange or brown.

Electron Treatment:
Electrons are accelerated in to the diamond, again only skin deep and produce a blue to blue/green colour. heat treatment produces orange-yellow, pink- mauve, and brown.

Gamma Ray:
Not used today due to its slow effects taking months to colour a stone. Produces permanent blue and blueish-green colours.

Neutron Treatment:
This is the most common form of irradiation used today. The diamonds are bombarded in a nuclear reactor and produce permanent green. When heated, yellow, orange, brown, pink and mauve colours may be produced.

Radium:
Produces colours from alpha, beta, and gamma radiation, but is not used as stones are left radioactive.

Evidence of treatment:
If you should ever consider buying a coloured diamond have it checked by a reputable laboratory to ascertain whether the colour is natural or otherwise. The difference in price is vast. A report may also indicate its permanance.

Diamond is formed at great depth in the earth, between 150 and 300 km below the surface and at great temperatures and pressures. By a kind of volcanic eruption the diamonds were pushed up through volcanic pipes of diamond bearing rock such as kimberlite. With gradual erosion kimberlite chimneys were exposed at the earths surface.

Peridotitic (Crystal Form)	Eclogotic (Crystal form)	Epigenetic Inclusions (powder form)	Inclusions of uncertain origin
Olivine	Omphacite	Serpentine	Amphibole
Enstatite	Garnet	Graphite	Magneteite
Diopside	Kyanite	Hematite	Feldspar
Garnet	Ilmenite	Goethite	Mica
Spinel	Chromite	Kaolinite
Ilmenite	Sulphides
sulphides	Coesite
Zircon	Diamond
Diamond	Ruby
	Rutile