Diamond

Colour and varieties

Colourless (white); pale yellow, pale brown, pale green or grey.
Fancy colours (those of a distinct colour) including yellow and brown; rarely green, pink, blue and black; very rarely red and purple.

Commercially, diamond is the most important of all gem species. It is estimated that diamonds account for approximately 90% of the value of gemstones purchased thoughout the world. Diamond is faceted to display its unique combination of adamantine lustre and fire. This fire is a direct result of the high disperaion (0.044) of diamond. Diamond displays a higher degree of dispersion than any other natural colourless gemstone.
A pure diamond is composed entirely of carbon and is colourless. However, diamond crystals usually contain trace elements, the most common of which is nitrogen; this causes the pale yellow colour often seen in natural diamonds. A much rarer trace element in diamond is boron which causes a blue colour.
However, not all diamonds are coloured by trace elements. Brown and pink diamonds owe their colour to defects in the crystal structure and green diamonds are the result of vacancies (holes) in the crystal structure. These causes of colour are covered more fully in the IDT Graduate Gemologist Diploma Course.

Localities

The alluvial deposits of India and Borneo were the only known sources of diamond from classical times until the eighteenth century. The important Brazilian fields were discovered in about 1725.
The alluvial and kimberlite pipe deposits of South Africa were discovered in the latter half of the nineteenth century, and those in Siberia during the 1950s. In the 1980s Australia became an important producer of diamonds and the most recent important commercial discovery was in Canada where mining began in the late 1990s.
The important gem diamond-producing countries today include Angola, Australia, Botswana, Brazil Canada, China, Congo, Namibia, Russia, Sierra, Leone, South Africa and Tanzania.
Diamond is the bithstone for April.
Many of the myths surrounding diamonds originated in India and have been passed on and adapted as diamonds reached Europe.
Ancient Hindu lapidaries warn against the wearing of flawed diamonds as this could bring misfortune, whereas: “He who has a pure body, and carries on his person a diamond that is sharp-pointed, without blemish and entirely flawless, shall daily increase his worth in happiness, prosperity, children, wealth, crops, cows and livestock, to the end of his life.”
In the West, most Medieval authors state that diamond has the power to protect against poisons, although others believed it to be a poison.
Diamonds have also been associated with love, but this image and their use in engagement rings has only become common place relatively recently. This is primarily due to the rarity of diamonds prior to the African finds in the late nineteenth century and a widespread advertising campaign started by De Beers in the late 1930s.

Occurrence and crystal habit

The octahedron form is a common habit for diamond. Some more complex forms also occur, including the dodecahedron, frequently with rounded faces, and the traingular twinned crystals called ‘macles’. Triangular pits – trigons – may be seen on octahedral faces.
Although diamonds are found in diamond-bearing volcanic pipes, they do not form within them. The diamonds form in the mantle and are captured by the molten magma as it drives its way up through the upper matle rocks capturing diamonds from the walls of the rocks through which it passes. The volcanic rocks in which diamonds occur are called kimberlite and lamproite. Although not all such rock contains diamond, other gemstones such as garnet and spinel may be present, and their occurrence is often a useful indicator of the possible presence of diamond.
The industry’s procedure for extracting diamonds is different from that used for all other gemstones. The object of mining the ‘coloured stones’ (i.e gems other than daimond) is to extract only the stones of gem quality, whereas all diamonds can be useful regardless of quality or size. Those diamonds not of gem quality, wheras all diamonds can be useful regardless of quality or size. Those diamonds not of gem quality, the majority in terms of quantity, are used in a huge variety of industrial applications. Consequently, diamonds are prospected for and extracted on a mcuh larger scale and in a far more systematic, mechanized way than any other gem materials.
Diamonds are mined either from volcanic bodies of kimberlite or similar rock, or from the river and beach gravels where they accumulated after erosion from these rocks. Since gem-quality diamonds fetch a much higher price than industrial grade diamonds, a deposit must contain a sufficiently high proportion of gem grade material to make it economically worth mining. In an average economic deposit, 100 tonnes (100 million grams) of kimberlite ore would contain about 25 carats (5 grams) of diamonds, of which just 5 Carats (1 gram) may be gem quality.
More information can be found in section 10 about diamond mining and procedures now in place to prevent the exportation of Conflict Diamonds.

Durability and fashioning

Diamond is the hardest known natural substance and is faceted to display its unique combination of adamantine lustre and fire. Its supreme hardness ensures a lasting precision of cut, unique among gemstones. Most cut diamonds display knife-sharp facet edges and absolutely flat facets.
Although diamond has a hardness of 10 on Moh’s scale, it lacks the toughness of some stones due to its cleavage. The perfect octahedral cleavage in diamond may be exploited in the fashioning of diamond to split large crystals or trim off flawed material. Cleavage is seen in and on cut and rough stones.
The hardness of diamond varies according to the crystallographic orientation. But, in any direction, diamond is still much harder than any other gemstone. The hardness of diamond requries the application of special techniques in the cutting process, this along with the precision, in terms of proportions and angles, with which the stones must be cut demands a high degree of skill from the diamond cutter. Diamond is normally faceted but very occasionally uncut crystals are set.
The most popular cut for diamond is the round brilliant. The 57 facets (58 with the culet) of the well-proportioned brilliant cut are polished at specific angles relative to one another. This cut is designed to show the optical effects of brilliance (reflection) and dispersion to their best advantage. Diamond manufacture involves four basic stages: designing, cleaving or sawing, bruting and polishing.
In designing the brilliant cut, facets are angled to maximize brilliance and fire. The angle between pavilion facets and the girdle is the most important; if the pavilion depth of the stone is either too deep or too shallow then light is not returned to the eye reducing the brilliance of the stone. Changing the crown angle, or height, and thus the table size will alter the balance of brilliance and fire seen in the stone. See section 11.
Many other cuts are also used for diamonds including other brilliant cuts such as the square, pear, marquise and oval. The emerald and step cuts are also used. Baguettes and tapered baguettes are modifications of the step cut, typically used for small stones. Older styles of cut include the rose cut with a flat base and a dome of triangular facets; this style of cut is found mainly in antique jewellery. New desighns in diamond manugacture frequently appear, with a drive towards increased variety and choice for the customer and increased yield from the rough.

General Care

Diamonds attract grease so avoid applying hand creams or soaps whilst wearing. Although hard, diamond possesses perfect cleavage: if knocked in the wrong direction it can cleave/fracture, so avoid sharp knocks.

Workshop Care

Burning; if using heat first coat the stones to protect against oxidizing conditions
The jewellers’ torch, particularly if the stone has been filled.
Ultrasonic and steam cleaners if the stone is heavily fractured or lead-glass filled.