The word "diamond" comes from an ancient Greek word meaning "incorruptible." Well before lapidaries -- or stonecutters -- learnt to turn raw diamond into the brilliant faceted gems that fill jewellery stores today, people valued the stone for its hardness. Modern industries use diamond as a durable cutter and abrasive. Gem-quality diamonds look little like industrial-quality diamonds; no one would mistake humble grains of abrasive grit for gemstones.
Clarity separates gem diamonds from industrial diamonds. Virtually all industrial-grade diamond is translucent or opaque instead of the transparency required of gemstones. Diamonds used in industry more closely resemble jagged sand or gravel than the clear faceted stones in a jeweller's shop. Such stones would cost more to work into gems than they would bring on the retail market.
Industrial diamonds vary in hue from off-white to nearly black. While colourless white gem-quality diamonds and attractive hues like canary yellow, pink and blue command the highest prices, the colours of industrial diamonds typically don't matter. A murky grey diamond scrapes a surface as efficiently as a clear specimen would. The line of demarcation between industrial-grade diamonds and gem-quality diamonds varies with fashion. Marketers may sell stones that would once have found their way into barrels of industrial abrasive as "chocolate diamonds" or "cognac diamonds," but only if the stones have gem-worthy clarity.
Stonecutters shape commercial gem-quality diamonds into recognisable forms, all of which exhibit radial or bilateral symmetry. Drawing an imaginary line down the centre of a heart-shaped or teardrop diamond should produce two halves that mirror one another in shape, size and curvature. Like other naturally occurring crystals, diamonds may not form symmetrically; distorted shapes that a lapidary cannot polish into smaller symmetrical gems become industrial diamonds.
A diamond's hardness allows it to cut any other substance including other diamonds. The abrasive grit that diamond cutters use to polish facets comprises other diamonds. The diamond dust that wears away becomes more grit for polishing, so nothing of the stones goes to waste. While larger diamonds may serve industrial purposes as drill bits or tiny anvils for research and manufacturing, most industrial diamonds are no larger than grains of sand. Gem-quality diamonds become exponentially more valuable the larger they are.
Jewellers and investors prize natural diamonds over synthetic ones; industrial diamonds' synthetic origins can increase their cost. Synthetic stones remain free of the microscopic fracture lines and weaknesses that natural stones may have. For anvil stones and drill bits, fracture-free diamonds cost more. Growing synthetic diamonds also ensures consistent size and shape, making them preferable for delicate grinding and polishing tasks. The manufacturing process of synthetic stones leaves impurities that tint them; while this affects the price of a gem, it doesn't matter for a drill bit.