Rough Diamond Guide Rough Diamond Sorting

Rough Diamond Sorting and Classification

Principal Crystalline Diamond Shapes
Rough Diamond Classifications
Gem Quality Diamond
Industrial Quality Diamond
Crushing-Boart or Boart
Rough Diamonds Photos

Principal Crystalline Diamond Shapes

Diamond crystallizes in the cubic system and its crystalline shapes are thus numerous, the principal ones are:

Octahedron
Dodecahedron
Cube
Rhombododecahedron

Rough Diamond Classifications

After diamond was recovered, it will have to be sorted according to certain categories before being sold:

Diamonds for Cleavage
Diamonds for Sawing
Diamonds for Cutting
Industrial Diamonds

Rough diamond can be sorted according to 3 distinct categories:

Gem Quality
Industrial Quality
Crushing-Boart or Boart

Only 20 % of the world production of rough diamonds are intended for the jewellery (gem quality) and 80 % for the industrial uses. There would be more than 5,000 possible rough diamond classifications.

Gem Quality Diamond

It is this type of quality which will be used in the jewellery industry.

It must be of good color and of good clarity, its shape is not very important because the diamond must be cut.

This category of diamond requires a classification of the stones by subcategories.

Images from diamondrough.com

Stones: very beautiful stone of more than 1 carat.
Fancy Colors stones are those with color that does not lies between the bluish white and the yellowish. The color of fancy colors diamonds (colored diamonds) is blue, green, pink, yellow, brown, etc...
Closed stones: are monocrystals, beautiful shapes, good for sawing and polishing.
Spotted stones: are monocrystals, beautiful shapes, these stones have inclusions but it is possible to make them disappear with the cutting.
Naats: are deformations of crystallizations, they must be cleaved or bruted.
Irregular stones: are octahedral or dodecahedral (irregular shapes), they are directly cut.
Cleavable stones: they must be cleaved.
Coated stones: the industry have named coated stones « speculation stones ». A gangue or a film covers them hiding the interior of the stone. They can remain opaque or let appear a beautiful stone.
Frosted stones: are identical to coated, but the film is translucent.
Milky stones: as its name indicates, this stone has a milky aspect.
Blocks: of a particular shape, their crystallographic orientation is difficult to see.
Plats: in fact generally macles are very often employed for the rose cut.
Sands: they are very small stones (less than 0.10 carat), mostly used for the size 8/8
Commons Goods: they are of a very poor quality and they are the extreme product of the gem quality.
Rejections Stones: they are of very bad quality and therefore must be eliminated.

Industrial Quality Diamond

As its name indicates, it is the quality of diamond which is reserved for industry.

Industrial diamonds must nevertheless be of a good quality.

The yellow color is preferred because of a greater hardness.

One classifies them according to the weight, lower than 3 carats, but also according to their number of point. One uses them for example for the manufacture of dies, the tools for drilling, etc...