Of the diamond’s two allotropes—carbon and graphite—the former is known for its harness and high light dispersal render it fit for industrial applications and jewelry making. Due to its excellent abrasive quality, diamonds can only be scratched by fellow diamonds. This means that not only do they sustain polish well but also retain their luster. Each year, about 130 million carats (26,000 kg) of diamonds are mined, valued at US$ 9 billion. Further, each year almost four times the mass of natural diamonds are produced as synthetic diamonds, though not of the best quality.
The origin of the word “diamond” is from the ancient Greek adamas meaning “impossible to tame.” In India, they were used as religious icons and were therefore prized as gems—and that was at least 2,500 years ago! Over the centuries, cutting and polishing techniques improved to such an extent that in the 19th century these gems were very popular and came to be judged by the “four Cs”—carat, clarity, color, and cut.
The natural home of diamonds has traditionally been central and southern Africa, though this mineral has also been discovered in large quantities in Canada, Russia, Brazil, and Australia. Mined from volcanic pipes deep in the recesses of the earth, diamonds are born when carbon-containing materials are exposed for long to high pressure and temperature. These then form diamond crystals.
This is possible since under the continental crust, diamonds begin to form at an initial depth of 150 km (90 miles), with a pressure of nearly 5 gigapascals and a temperature of nearly 1200°C (2200°F). However, diamonds under the oceanic crust take shape at much greater depths because they need higher temperatures and pressure. After long periods of exposure to equally high pressures and temperatures, diamond crystals grow larger in size.