How Are Natural Diamonds Formed?
Diamonds are made of pure carbon. Natural diamonds are formed in volcanoes, where tremendous heat and pressure act on the carbon found in the molten rock.
Most natural diamonds are formed at depths of 140 to 190 kilometers in the Earth’s mantle. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years (25% to 75% of the age of the Earth).
The pressure and heat slowly change the carbon into diamonds. Today, most diamonds are mined from deep within the earth, and are found in rock that formed when these volcanoes cooled down.
Diamonds are not naturally beautiful. Most look like dull pieces of glass when they are mined. To become glittering jewels, the rough diamonds must be intricately cut and highly polished.