Once in a while, a columnist has to tackle a particularly hard topic. This week, I tackle the hardest topic of all: diamonds.
Diamonds have been much on my mind recently for a variety of reasons, not least because of watching a spate of romantic movies. It is perhaps a sad commentary on the way my mind works that, while watching a touching scene involving the bestowing of a diamond ring, instead of thinking, “How sweet,” I was thinking, “Ah-ha! Next week’s column!”
Diamonds aren’t anything fancy, chemically: they’re just carbon, like coal or a charcoal briquette. But the carbon molecules that make up a diamond are much more tightly organized than in a lump of coal, close-packed in rigid geometric fashion, and it’s that tight organization that give diamonds their special characteristics.
To begin with, diamond is the hardest substance known. Hardness is defined as resistance to scratching. The only thing that can scratch a diamond is another diamond.
From an industrial point of view, the hardness of diamond is its most important characteristic. Most diamonds aren’t large enough or of high enough quality to use for jewelry. Instead, they’re used for a variety of applications from cutting other diamonds to drilling for oil to cutting glass to making fine wire (by forcing thick wire through a graduated series of diamonds with tiny holes drilled in them).
Another characteristic of diamond that’s valuable in industry is its ability to conduct heat rapidly. As a result, a real diamond always feels cold (one way to distinguish a real diamond from a glass copy, should you have your doubts about that ring your boyfriend just gave you). Recently, scientists have developed methods of depositing thin films of diamond on objects. Diamond coatings on high-powered computer chips help them rapidly dissipate the heat that could otherwise cripple them.
Even though most diamonds are used industrially, most people think of diamonds as gemstones, not drillbits. Two other characteristics of diamonds have made them the most prized of all jewels through the ages: brilliancy and fire.
Diamonds are brilliant because they have a very high index of refraction, higher than that of any other natural, transparent, colourless stone. That means that almost all the light that enters a well-cut diamond is sharply bent and thrown out again to delight the eye. “Fire” is a result of diamonds’ strong dispersion, its ability to separate white light into the various colours of the spectrum. Not only does almost all the light that enters the stone get tossed out again, it gets tossed out in a spectacular, multi-coloured flash.
Brilliancy and fire are not immediately apparent in diamonds found in rough, uncut state. In fact, some forms of naturally-occurring diamond wouldn’t be recognized as diamond at all by most people: bort, ballas and carbonado. Bort is imperfectly crystallized diamond, very hard, but dark in colour. Ballas is a compact, spherical mass of tiny diamond crystals. Carbonado is opaque, and grayish or black.
Even gemstone-quality diamonds aren’t always immediately recognizable. The diamond rush in South Africa in 1866 began when a child picked up a pebble on the banks of the Orange River. Some astute grown-up eventually recognized the “pebble” as a 21-carat diamond.
Cutting and polishing a rough diamond is, as you might expect, a tricky business. The goal is to produce the largest, highest-quality gem or gems possible.
The trickiest method of cutting a large diamond is cleaving. The diamond has certain natural cleavage planes through it which the diamond cutter identifies and marks. Then, using a mallet and a kind of chisel, he attempts to cause the diamond to split along the cleavage plane he has chosen. Too hard a blow, or a blow in the wrong place, and the stone can be ruined.
Most diamonds today are cut by a thin metal saw, its edge charged with diamond dust and oil, instead of by cleavage.
Once the diamond is cut, the facets must be formed. This is called polishing, and again the instrument used is a spinning metal wheel, this time with its surface instead of its edge charged with diamond dust and oil. The most common cut of diamond, the brilliant, has 58 facets.
How much the cut diamond is worth depends on four criteria. First is colour. “White,” or absolutely transparent, diamonds are much sought after, but may diamonds have a slight colour from impurities in the carbon. Rare and beautiful colours, such as red, can boost a diamond’s value immensely.
The second criteria is how well the diamond has been cut and polished. The third criteria is the presence or absence of internal blemishes and flaws and of external chips. The fourth criteria is the weight.
Diamonds and other gems are weighed using the metric carat, which is equal to 0.2 grams. A five-carat diamond, therefore, weighs one gram.
The largest diamond ever found was the Cullinan, discovered in South Africa in 1905 and presented to King Edward VII by the government of the Transvaal. It weighed an astonishing 3,106 carats–621.2 grams, or 1.37 pounds, if you prefer–before being cut into a total of 105 gems. The largest of them is a 530.2-carat drop-shaped stone called the Star of Africa, now set in the British royal scepter. It’s the largest cut diamond in existence.
Diamonds are apparently formed under conditions of incredible heat and pressure deep in the Earth. They’re usually found in conjunction with pipes of a mineral called kimberlite, apparently volcanic in origin, so the theory is that sudden uprushes of molten rock from far underground brings diamonds to the surface. Tiny diamonds are also sometimes found in meteorites, apparently formed in the moment of impact.
Although we’ve learned to synthesize diamonds for industrial purposes in the lab, a synthesized gemstone would cost more to make than it would be worth. Barring a cheap way to synthesize diamonds, people have instead found ways to simulate them. The cheapest method is “paste,” actually a form of lead glass, cut and polished or moulded into shape. Rock crystal, a form of quartz, can be cut into imitation diamonds called rhinestones. Zircons have good fire and can be made almost colourless, and various synthetic minerals can also be used to simulate diamonds–but all can be detected by one simple test: a real diamond will scratch them easily, and they can’t do a thing to the diamond.
Those, I’m afraid, are just the cold, hard facts.
