Gem diamonds: from 0.005 to 3,000 carats (Part two of three)

Some of the smallest gem diamonds weigh no more than one-200th of a carat. They are known as “half-pointers.”

Though not measuring much over a millimetre, stones half that size are also produced. They are known as “quarter-pointers.” (A “point” is the diamond dealer’s measure for a 100th of a carat.)

They are cut from stones classified as “near gem,” the polisher’s skill removing the tinted, lower-grade material from the sliver of gem-quality stone.

The industry employs 300,000-400,000 persons in India. Bombay is now one of the world’s major diamond centres.

The largest diamond ever found was the Cullinan. It was found in the pit-wall of South Africa’s Premier mine in 1905. In its uncut state, it was about the size of a child’s fist and weighed 3,106 carats (621.2 grams, or 1.4 lb.). Interestingly, the Cullinan is a cleaved stone and for many years there was hope of finding its missing part.

The present company policy of offering a reward for stones picked up on the property may well hark back to that time. The policy applies to employees only; visitors need not make a claim.

The Premier mine is 50 km east of Pretoria, South Africa, and is one of world’s few underground diamond mines. There are only six operations in this category. The other five are also in South Africa.

By far, the largest proportion of the world’s diamonds comes from open pits and alluvials.

All of Russia’s diamonds are recovered from a series of open pits scattered on either side of the Arctic Circle. The first discovery was made in 1954, fittingly enough by a woman geologist. Forty kimberlite pipes were found in the following two years and there have been many others since then. Operating conditions verge on the unbelievable. Temperatures drop to 56C for seven months of the year. Permafrost reaches to 300 metres in some locations, turning overburden into rock. Normal diesel fuel freezes solid and, according to reports of infrequent visitors, dipper sticks of the first power shovels snapped like toothpicks because of the cold.

Separating diamonds from the massive volumes of kimberlite waste rock generally requires equally large volumes of water. Too much water would have been intolerable under Siberian climatic conditions. Consequently, the Soviet scientific community was directed to find a better way during the Stalinist era. It did. The scientists developed the X-ray method for concentrating diamonds, a technique now used the world over.

It was the first major improvement in recovery methods since the invention of the grease-table in 1896 (diamonds stick to grease as flies do to fly-paper).

Siberian diamonds are small but high quality. Gemstones are reported to constitute up to 40% of the mines’ output — an unusually high proportion. Practically all gemstones were sold on the western market through De Beers during the Soviet regime but the industrials were kept for national consumption. The Russians are believed to be the world’s largest users of industrial diamonds.

Another unusual source of high-quality stones is the 480 km of Atlantic beach sands on Africa’s southwestern coast. So rich were the earliest discoveries (1906) that mining and recovery needed no more than gangs of men crawling on hands and knees across the sand using their fingers and thumbs. Today’s operations are massive sand-moving operations. Yet once bedrock is laid bare, manual labor must still be used to recover stones lodged in the bedrock’s potholes and crevices. The bulk of the sand overburden is pay-dirt and goes directly to the recovery plant.

Of the stones, 95% are gem quality. Experts agree the structurally weaker industrial stones were degraded to dust, either by the ocean’s pounding or the journey of several hundred kilometres from their inland source. All that remain are high-quality gems.

In the hands of Ernest Oppenheimer, the beach deposits played a vital role in the creation of De Beers’ diamond cartel.

Oppenheimer started his career as a diamond dealer. In 1917, he formed Anglo American (LSE). Between 1919 and 1921, he purchased key locations on the beach alluvials and with the leverage of this abundance of easily mined gems, he secured control of De Beers. The all-powerful Central Selling Organization, a marketing agency, was subsequently formed in 1930. The cartel controls the sale of more than 80% of the world’s rough gem diamonds.