Composition: C
crystal System: Cubic
Habit: Mainly Octahedral, but also in Cubeas, Dodecahedra, and modifications of these, twinned octahedra "Macles"
Varieties: Type I Diamonds contain Nitrogen as the main impurity.  Type Ia contain Nitrogen atoms in clusters, this does not affect the stone's colour, Type Ib contain Nitrogen atoms dispersed throughout the diamond crystal lattice which causes the yellow colour we refer to as Cape Series Diamonds.  Type II Diamond contain no Nitrogem impurities at all. Type IIa contain no other impurity and is rare in nature.  Type IIb Diamonds are very rare and contain Boron atoms which replace carbon atoms and make the stones electrically semi-conductors, many Type IIb Diamonds are often blue, but Diamonds that ae coloured blue by irradiation are of type I and nnot therefore semi-conductors.
Refractive Index:  2.417
Dispersion: Hign (0.044)
Specific Gravity: 3.52
Hardness:  10
Cleavage: Perfect (Octahedral .. four directions)
Fracture: Conchoidal or irregular
Lustre: Adamantine.
Absorption Spectrum: Colourless to yellow cape series diamonds have a band at 415.5nm plus other weak bands in the violet, Brown series diamonds have a band at 504nm with also sometimes two weaker bands in this area.
Inclusions: Crystal inclusions include hematite, diamond, diopside, enstatite, garnet, olivine and Zircon. Black inclusions may be iron ores or graphite.
Occurrence: South Africa, Namibia, Western Australia, Brazil, China, USSR

Diamond

The traditional round cut provides a combination of the best qualities a diamond can have. The symmetry of this shape means it is capable of reflecting nearly all of the light that enters it and it therefore has the greatest potential for exuding diamond hue and brilliance. There are also other shapes that can emphasise a diamond's different features. The choice of a shape is best based on personal taste and the design of the jewellery.

No two diamonds are the same. A diamond's most distinguishing characteristics are its inclusions or marks that are often invisible to the naked eye. However, under a jeweller's magnifying loupe or microscope they can look like crystals, tiny rivers, or clouds. A diamond's clarity is determined by the presence or absence of inclusions, the fewer inclusions mean better clarity, and how visible they are. The greater a diamond's clarity, the greater its brilliance and value. A diamond categorised as internally flawless will have no inclusions, but this is extremely rare. Diamonds with very, very small inclusions are graded as VVS1 or VVS2. Those with larger inclusions appear lower down the grading skill. Diamonds with inclusions that are visible with the naked eye are graded I1 to I3.

A diamond's weight is measured in carats, with one carat being equivalent to 100 points. You will often see a diamond referred to as a 3/4-carat stone or a 75-point diamond. Larger stones are often more highly valued, but size should not be the only consideration,clarity, cut, and colour grade, will all impact the desirability and value of a diamond.

Diamond is the hardest known naturally occurring mineral known to man, this with it's high dispersion of light make it useful for industry and for the use in jewellery. So named because of it's hardness derived from the ancient Greek  (adamas) "invicible" "unconquerable" There is nothing to compare to it's hardness and therefore is nearly imperishable, it's cutting resistance is nearly 140 times greater that that of Corundum (Sapphire & Ruby)
Almost half of the worlds Diamonds originate from South Africa, with other sources being India, Russia, Canada, Brazil and Australia. They are mined from Kimberlite and Lamproite volcanic pipes which bring the diamond crystals to the surface from deep within the earth where they were form millions of years ago under high pressures and temperatures.

The cut of Diamonds determines how it reflects light, which is responsible for its sparkle or scintillation and brilliance and refers to the angles and proportions of the polished stone. A well cut diamond is cut by skilled professionals to the very best proportions possible so that the light will be refected from each of its mirror like facets and dispersed through the top.  Too shallow a cut will let light escape through the diamonds pavillion, causing it to appear dull, while to deeper a cut will allow light to be lost through  the diamonds sides. making it appear dark.  It is only one of the 4 C's that is not created naturally by mother earth, but is geneated by the skill of the most experienced craftsmen. Cut is often also used in reference to the physical shape of a Diamond.
Because a Diamond with perfect colour and clairty could nevertheless have poor brilliance if it is not well cut, many gemmologists consider this to be the most important property to note when choosing a Diamond.  because a Diamond with perfcet colour and claity could nevertheless have poor brilliance if it is not cut well, many gemmologists consider this to be the most important property to note when choosing a Diamond

Because of it's value, diamond is probably the mos imitated of all the gemstones, unlike Emerald, Ruby and Alexandrite, whose value sometimes well exceeds that of Diamond.  Diamond simulants include natural gemstones such as the colourless varieties of Quartz, topaz, Corundum and Zircon, all of which can be distinguished from Diamond by their doule refraction, with the exception of Zircon it is possible to identify all these stones on the refractometer, and Zircon can be illimanated by it's high double refraction.