The hardest substance on Earth

A diamond is the hardest natural substance on earth. If it is placed in an oven and the temperature is raised to about 763 degrees Celsius (1405 degrees Fahrenheit), it will simply vanish, without even ash remaining. Diamonds are formed over a period of a billion or more years deep within earth’s crust, about 150km (90 miles) deep, and is pushed to the surface by volcanoes. Most diamonds are found in volcanic rock or in the sea after having been carried away by rivers when they were pushed to the surface. A diamond is 58 times harder than the next hardest mineral on earth, corundum, from which rubies and sapphires are formed. It was only during the 15th century that it was discovered that the only way to cut diamonds was with other diamonds. It's a fact that not all diamonds are white. Impurities lend diamonds a shade of blue, red, orange, yellow, green and even black. Vivid blue, green and pink mined diamonds are the rarest. They are not the rarest gemstones, however. That title goes to a pure red ruby. Diamonds actually are found in abundance; thousands are mined every year. 80% of them are not suitable for jewelery, they are used in industry or in cheap rings.