MINING DIAMONDS

Of all the diamonds mined in the world each year, less than half are gem quality; the rest fall into two other main categories known as near-gem quality and industrial quality diamonds.

Gem quality diamonds display a high standard of excellence in quality and are used in jewellery. The clarity of these diamonds ranges from flawless through to visible inclusions.

Near-gem quality diamonds represent those stones of a quality between gem and industrial, that in fact can be used as either depending on the individual stone. These stones have clarity grades ranging from visible inclusions through to industrial.

Industrial quality diamonds are low quality or badly included stones and are suitable only for industrial use; for example, they are used in dentist's drills and earthmoving equipment.

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Diamond Mining
Diamonds are recovered by way of pipe or alluvial mining.

Pipe Mining
Pipe mining refers to the extraction of diamonds from volcanic pipes. Typically, a very large area has to be covered. An average of 250 tonnes of ore must be mined in order to produce a one-carat gem quality polished diamond.

In most countries, a diamond pipe mine is composed of kimberlite, or blue ground. Initially kimberlite is dug from the surface of the pipes in rough opencast mining. Once the surface deposits have been exhausted, shafts are sunk into the ground at the edge of the pipes, and tunnels are driven into the deeper parts of the pipes. After the diamond-bearing rock is brought to the surface, it is then transported to a screening plant where the diamonds are separated from the host rock.

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Alluvial Mining
This process involves the extraction of diamonds from riverbeds or ocean beaches. Millions of years ago, at the time the diamond pipes were formed, some diamonds were weathered out of the pipes and carried great distances along rivers and even into oceans.

In order to extract these diamonds from beaches, a wall is built to hold back the surf. Up to 25 metres of sand is bulldozed aside to reach the diamond-bearing level. Once reached, the diamond-bearing earth is removed and transported to screening plants.

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Diamond Cutting and Polishing
The history of diamond cutting and polishing has its origins in India, where it was discovered a long time ago by Indian lapidaries that a diamond could be made to glisten simply by grinding another diamond against it.

Nowadays the diamond and its powder play an important role in the cutting and polishing of diamonds. Over time modern machinery has replaced traditional diamond cutting tools.

Diamond cutting and polishing requires anywhere from several hours to several months to complete. During this process, a diamond will lose on average half of its original weight.

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Diamond Cutting
As every diamond is different, a stone must first be carefully examined by the cutter and then marked for cutting. Of all the cuts, the most popular is the round brilliant because of its ability to give a stone the greatest possible brilliance and fire with the most minimal amount of weight loss. The following cutting and polishing procedures uses the round brilliant cut as an example.

The rough diamond is divided into two parts by sawing or cleaving. Most stones are sawn across the "grain" (visible evidence of the diamond's crystal structure) by a paper-thin metal disc coated with diamond dust revolving at high speed or by laser. The stones that are marked for cleaving are split along the grain by a single blow from a steel blade.

After cleaving or sawing, the corners of the diamond are rounded off by a process known as bruting or girdling (only round brilliant cuts require this step). The stone is cemented into a "lathe", a holder that fits on a turning shaft. Another diamond is cemented to the end of a long rod held under the bruter's arm. As the lathe rotates, the two diamonds are brought together and grinded to shape. Diamond dust is produced from this action and is used in further sawing and faceting.

The brilliant now has a girdle-a sort of rim at the widest part by which it is usually set. The size or position of the girdle should not change throughout the rest of the diamond cutting process.

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Diamond Polishing
The polishing of the diamond begins; one by one, facets will be ground on to the stone. A facet is the tiny plane or surface that traps the light and makes a diamond sparkle. Most diamond cuts have 58 facets.

The facets are applied to the diamond on a "turntable", made of porous iron, which has been coated with diamond dust and oil. The diamond is set into a holder and held against the turntable as it revolves at a very high speed.

A diamond has been cut well when its facets are clean, sharp, and symmetrical, and the proportions above and below the girdle are correct. A diamond is correctly proportioned when one-third of the total weight of the gem is above the girdle and two thirds below. A well-cut diamond will be fiery, brilliant and beautiful.

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