Market Basics » Diamonds
A diamond consists of carbon atoms which are linked in a regular three-dimensional lattice with a repeating or crystalline pattern. Diamonds belong to the cubic, or 'isometric' crystal system. Diamonds are the most popular and precious of all of the world's gemstones.
Diamonds can also be created synthetically.
Due to their beauty, which is largely a result of their ability to refract light, diamonds are often referred to as "the gem of gems". Diamonds also possess unique properties, most notably their exceptional hardness, that make them useful in industrial, medical and scientific applications.
Natural diamonds were formed under very high temperatures (between 900 and 1300 degrees Celsius) and great pressure. Carbon atoms combined to crystallise and grow as diamonds within rocks.
Diamonds are not as rare as marketing agents suggest.
The metric carats denominated in US dollars and cents. The carat is a unit of mass equal to 200 mg (0.007055 oz).
The carat is divisible into one hundred points of two milligrams each. Other subdivisions, and slightly different mass values, have been used in the past in different locations.
A paragon is a flawless diamond of at least 100 carats (20 g).
Ct. The ANSI X.12 EDI standard abbreviation for the carat is CD.
Avenues of trade
The majority of diamonds are sold as "rough" or uncut stones transacted between miners and wholesale dealers on a "willing-buyer willing-seller" basis.
"On market" rough diamond sales are conducted ten times per year in line with the industry's market cycle. They take place in Antwerp where customers can view product and discuss their requirements.
Antwerp is the global centre for the wholesale trade in rough diamonds. 60% of the global trade in rough goods passes through the city. An estimated 50% of all polished stones pass through Antwerp.
The Antwerp Diamond Bourse is the central clearing house for rough and polished stones. The 'mazal' or binding handclasp fixes price, delivery and conditions.
"Off market" sales, generally associated with "blood diamonds" take place informally between diggers and intermediaries close to the mine site.
Southern Africa produces the majority of the world's diamonds, but there is also diamond production in Russia, Canada, Australia, India, China and South America.
Based on 2006 Kimberley Process production statistics, Botswana is the world's biggest producer of diamonds by value, followed by Russia, Canada, South Africa and Angola.
Mumbai is a cutting and polishing centre that is estimated to handle two-thirds of the world's gems, the majority of which are an inferior quality to those processed in Antwerp.
Synthetic diamonds are becoming more popular.
The majority of diamonds are consumed in industrial applications such as grinding and cutting tools.
High quality stones are set aside for the jewellery market.
Extraction, Processing, Refinin, Classification & Supply Chain
Diamonds are mined using both open pit and underground mining. A limited amount of diamond mining takes place under water.
The principal activity in open pit mines involves the removal of overburden (rocks and soil above diamond-bearing rock) and the collection of diamondiferous ore. Ore in the pit is broken up by explosive blasting.
Excavators then load the rock into haul trucks. The trucks transport diamond-bearing ore to a primary crusher to commence the diamond extracting process.
Underground mining involves tunneling into the ground close to the diamond pipe to access the ore body. Tunnels are constructed on two levels, one above the other. Mining begins on the top level by blasting a slice of ore all the way across the ore body. Funnels are built to connect the top level tunnels with the bottom level so the broken rocks fall down to the tunnels below where they are collected by loaders. This method of underground mining is known as block caving.
How diamonds are processed
Ore from the mine is delivered to the process plant by haul trucks. Diamonds are liberated and recovered from the ore in six stages:
The mined material goes through a primary crusher that reduces it to a plant specific maximum size. The secondary crusher's product is conveyed to the primary stockpile. It is then conveyed to high pressure rolls-crushers, where its maximum size is reduced further.
Ore is then scrubbed and screened, where it is separated into three sizes. Oversized material is further reduced, and undersized material is rejected to the tailings dump. The remaining ore is conveyed to a Heavy Media Separation (HMS) Plant Feed Stockpile.
The majority of the material in the HMS stockpile is lamproite ore. It contains diamonds and some other high density minerals. The ore is then processed in a cyclonic separation plant. Heavy media consisting of ferrosilicon powder mixed with water is used to separate the lamproite ore from the diamonds and heavy minerals which sink to provide a diamond rich concentrate.
In the recovery plant, the diamond concentrate is fed through a series of custom-designed x-ray sorters. Diamonds fluoresce when exposed to x-rays. Sensors detect the flashes of light emitted by the diamonds. These send signals to the microprocessor that fires an air blaster valve at the appropriate moment, blowing the diamonds into a collection box.
The diamonds are finally acid-cleaned, washed, weighed and prepared for transport.
Three different cuts of polished diamond
Refractive index - 'Refractive index' ('R.I.'), is a measure of how well a substance can refract light. The R.I. of natural diamond is very high, at 2.4175. In addition, the R.I. does not vary very much from one diamond to another. The normal range of refractive indices for glass is between 1.50 and 1.70.
Life/brilliance - The 'life' of a polished diamond is regarded as the amount of light that is reflected back to the viewer. The term 'life' is also referred to as 'brilliance'. If the stone is cut to what are widely recognised as good proportions, for example if the facets have been polished at the correct angles, then brilliance will be increased.
Lustre - This is the surface gloss on a polished diamond, which to a large extent depends on the refractive index and quality of polish. Gemmologists describe diamond's brilliant lustre as adamantine: 'diamond-like'.
Very few gemstones have this type of lustre. Most well-known gemstones have a lustre that is described in one of the following ways: 'sub-adamantine', 'vitreous', or glassy, 'metallic', 'pearly', 'waxy', etc.
Fire - This is the play of colours that can be seen from the crown of a polished diamond. As light enters the diamond it is refracted and broken up into the colours of the spectrum and reflected back. The resulting rainbow-like colour flashes are called 'fire'.
Gemmologists and jewellers assess the physical attributes of diamonds using the 4Cs classification system - cut, carat, colour and clarity.
The 4Cs classification enables the comparison and valuation of diamonds. No one 'C' is more significant than another, and none will diminish in value over time.