Diamond scores #10 on the Mohs scale, and good is to excellent in toughness. Sources are South Africa, Australia, Brazil, Botswana, China, Canada, Ghana, Guyana, Indonesia, India, Namibia, Sierra Leon, Tanzania, Democratic Republic of the Congo, United States, Venezuela. India was the world’s only major source until the 18th century. Then Brazil’s alluvial deposits were discovered in the 1700’s. Both countries were overshadowed by South Africa’s enormous primary deposits, which appeared in the late 1800’s.
Diamond and graphite are both made of carbon. Diamond is a metastable allotrope of carbon. The difference between diamond and graphite lies in the way their carbon atoms fit together. This is caused by the different pressure and temperature conditions that exist when either mineral is being formed.
In a diamond, the atoms are arranged in tight three-dimensional patterns, bonded more strongly in all directions than that of graphite’s atoms, which are bonded in layers. Only under the right temperature and pressure conditions can diamonds be formed. The best temperature and pressure exists in very limited areas of the Earth’s upper mantle, between 90 miles and 140 miles beneath the surface. At that depth, those ideal conditions work together to force carbon atoms to form the extremely strong bonds found in diamond crystals. Diamonds that exist today were delivered to the surface between 2.5 billion and 20 million years ago. Diamonds themselves can’t be dated. Researchers, published in 2010, indicated that youngest known diamonds found in Brazil were just about 107 million years old.
Diamonds are especially precious and rare. The typically color is yellow, brown, and gray to colorless (D,E,F). Other colors, blue, green, black, translucent, pink, violet, purple, red are considered fancy colored diamonds. These colored diamonds are extremely rare, making them priceless. Just to give you an idea, a 35.56 cts blue, fancy colored diamond, once belonging to the King of Spain, was sold at Christie’s Auctions for 24 million dollars.