This video from National Geographic provides an overview of how diamonds are naturally formed. Professor Steve Haggerty, from Florida International University, appears throughout the video to explain different parts of the formation process.
 

Viewers are informed it was only in recent years that the natural formation of diamonds was discovered. Diamonds are formed from carbon, deep in the earth’s mantle – the layer between the earth’s crust and its extremely hot core.
 

Extreme pressure and temperature turns carbon into diamond. Diamonds are formed at around 1500 degrees centigrade (2700 Fahrenheit). The pressure at this depth is around 50 kilobars, the equivalent weight and pressure of over 4000 grown men standing on one of your feet.
 

Diamonds are pushed to the surface of the earth by a material called kimberlite, volcanic rock formed deep in the earth. Kimberlite is the host rock to diamonds and, along with mantle fragments, pushes diamonds to the earth’s surface. Small but violent volcanoes erupt and diamonds are found in the leftover rock formations.