Physical, Chemical and Optical Features

Diamond is formed in the upper mantle under high temperatures and pressures in ultrabasic igneous rocks – kimberlites, lamproites and komatiites. Diamond is the hardest known naturally occurring mineral and one of the hardest substances ever (harder substances include, for example, fullerite [see fullerenes], rhombohedral modifications of diamond, or nanocrystalline forms of diamond [ADNR]). It is a crystalline form of carbon. It consists mainly of individual crystals of octahedral, dodecahedral or cubic appearance. Diamond is beautiful and attractive to look at, because it has a number of unique and exceptional features.

Parameters of diamond

Diamond hardness

The name diamond derives from the Greek word adamas, meaning invincible. Diamond is the hardest naturally occurring material to appear on Earth. It is number ten on the ten-point Mohs scale, which measures the hardness of minerals. No. 9 is corundum (e.g. ruby, sapphire). Although there is only one-point difference on the scale, in fact diamond is 140 times harder than corundum. This qualitative difference is the same as the difference between points 1 and 9.

Diamond density

The density of diamond is 3.51g/cm3. Thanks to this property, diamonds have settled as alluvial deposits in river beds. Density is therefore the basic indicator in determining whether a gemstone is an actual diamond or an imitation.

Diamond thermal conductivity

The thermal conductivity of diamond is 6 times greater than that of copper. This property is used both in testing diamonds and in using diamonds in nanotechnologies.

Transparency and translucency

According to their translucency, we distinguish diamonds from the absolutely clear to the completely opaque. Only the best stones are put into jewels. Other diamonds are used in industry, where they play an indispensable role.

Fluorescence

This property of diamond was first used in the 1960s to sort diamonds. All diamonds exhibit fluorescence under X-ray and can be separated from the rest of the rock. Diamond fluorescence is usually blue, but may also be white, purple, yellow, green or orange.

The refractive index of diamond is measured at 2.417 and gives diamonds their unique optical properties that also serve to determine authenticity.

Dispersion

Dispersion is an optical property expressing the dependence of the refractive index on the wavelength (i.e. colour) of incoming light. The colour effects that can be seen in the protruding rays of light are caused by this property. Diamond has a low dispersion value of –0.044. Most synthetic stones with a comparable refractive index have a higher dispersion and the play of colours in these stones is unnaturally striking.

Scintillation and brilliance – the play of light. Sparkling brilliance is the number of reflections produced when the cut gemstone or light source is moved. The number of light reflections depends on the number of facets and their correct size.

Diamond colours

The white light around us is actually composed of a range of colours, ranging from red to violet. The resulting colour we see depends on what spectrum is absorbed or emitted. Almost all diamonds contain atoms of other elements. Most often they are nitrogen atoms. These cause a yellow colour, meaning that the blue spectrum is absorbed. Boron makes diamonds blue (it absorbs the yellow spectrum). Other colour mutations are caused by other mechanisms, such as crystal lattice deformation – pink diamonds, or radiation – green diamonds, and so on. Diamond without any other elements is completely colourless.