Diamond was first mined in India

The earliest diamonds were mined from stream gravels in the southern and central portions of India. An estimated 12 million carats (the carat is a unit of weight for gemstones equal to 0.2 gram) was produced from Indian mines. India was virtually the only source of diamonds until they were discovered in Brazil in 1725. East central Brazil has produced about 160,000 carats annually, chiefly from stream gravels near the city of Diamantina, Minas Gerais.

Today, about 95 percent of the world’s output of diamonds is from Africa.The Congo is by far the largest producer, supplying more than 50 percent of the global demand.

Source: "An introduction to Fossils and Minerals" by Jon