Diamonds (2002)

Few things say “Be My Valentine” more effectively than diamonds–reason enough to devote this week’s science column to these sparkling rocks.

Diamonds aren’t anything fancy, chemically: they’re just carbon, like coal. But their molecules close-packed in rigid geometric fashion, and that gives them special characteristics.

To begin with, diamond is the hardest substance known: the only thing that scratches diamond is diamond. Diamond also conduct heat rapidly, which is why a real diamond always feels cold (one way to distinguish a real diamond from a fake).

These two properties make diamonds extremely valuable for industrial purposes, but most people think of diamonds as gemstones, not drill bits. That’s because of two other characteristics of diamonds: brilliancy and fire.

Diamonds have a very high index of refraction, so almost all the light that enters a well-cut diamond is sharply bent and thrown out again to delight the eye; that’s brilliance. Diamonds also split that light into all the colours of the spectrum; that’s fire.

Diamonds are ancient, forming at about the same time as the continents, 200 kilometres or more beneath the surface where pressure of 5,520,000 kilopascals (800,000 psi) and temperatures between 1100 and 1482 degrees Celsius forced carbon molecules tightly together.

Diamonds are usually found in conjunction with pipes o kimberlite, thought to have formed at even greater depths than diamonds, then to have brought the diamonds with it as it rushed to the surface during volcanic eruptions.

To find diamonds prospectors first try to find kimberlite; however, most kimberlite deposits don’t contain diamonds, and fewer than one percent that do have enough to make them worth mining–but that tiny percentage includes those near Lac de Gras in the Northwest Territories, discovered by Canadian geologist Charles Fipke and associates after years of prospecting that began with locating minerals that are often associated with kimberlite pipes, then finding the pipes themselves, and finally confirming that they held enough quality diamonds to make open-pit mining economically viable. That led to Canada’s first diamond mine, which opened in mid-1998.

Today, there are plans to mine many more Canadian kimberlite deposits, possibly including those found here in Saskatchewan. Although the entire province is considered prospective ground for diamond exploration, most of the attention has been focused on the Fort à la Corne Kimberlite Province, a large area about 80 kilometres east of Prince Albert that is one of the largest clusters of kimberlite deposits (more than 70) in the world. Test results so far are so encouraging that there’s a good chance Saskatchewan may soon have its own diamond mine.

Of course, getting a diamond out of the ground is only one part of the process of turning it into the sparkling centrepiece of an unforgettable Valentine’s Day. You also have to cut and polish it.

The trickiest method of cutting involves identifying the diamonds natural cleavage planes, then hitting it with a hammer and chisel in the hope of causing it to split where desired. However, a too-hard or ill-aimed blow can ruin the stone, so most diamonds today are cut instead by a thin metal saw, charged with diamond dust and oil.

Polishing puts facets on the stone; it’s done by a spinning metal wheel with its surface charged with diamond dust and oil.

A cut diamond’s value depends on its colour (some diamonds have a slight colour due to impurities in the carbon; rare and beautiful colours, such as red, can boost a diamond’s value immensely), how well it has been cut and polished, how free it is of internal blemishes and flaws and external chips, and its weight, measured in metric carats (0.2 gram).

The largest diamond ever found was the Cullinan, discovered in South Africa in 1905 and presented to King Edward VII. It weighed 3,106 carats (621.2 grams, or 1.37 pounds) before being cut into 105 gems, the largest of which, a 530.2-carat (106.4 grams, or 3.4 ounces) drop-shaped stone called the Star of Africa, is now set in the British royal scepter. It’s the largest cut diamond in existence.

By contrast, the largest Saskatchewan diamond recovered to date weighs 0.985 carats–so if you have your heart set on buying your sweetheart a Saskatchewan diamond, you might want to wait a while.

With diamonds, as with all gifts, it’s the thought that counts–but it’s amazing how much more clearly a large diamond communicates the thought than a small one does.

Permanent link to this article: https://edwardwillett.com/2002/02/diamonds-2002/

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