Diamonds are the hardest natural substance on Earth, having been formed billions of years ago beneath the Earth's surface through a combination of tremendous pressure and extreme temperatures. Colored diamonds are most often yellow and brown, but in their pure state diamonds are colorless.
The earliest written account of diamonds dates back to around 500 B.C., but until the 18th century, the only diamond mines were in India. However, just as diamond production in India was dwindling, diamonds were discovered in Minas Gerais, Brazil, in 1725. As of 2015, Russia produces the most diamonds by volume, while Botswana is first in value of diamonds produced.