Black diamonds have always been a puzzle for geologists. Also known as carbonado, black diamonds are treated as something a little different from conventional diamonds.
First, black diamonds have unusual physical characteristics such as being composed of millions of diamond crystals stuck together and being porous as if formed in a gaseous froth. Traditional diamonds form as large crystals with classic crystal structure. Black diamonds look more like the obsidian (glassy black) or pumice (gray and full of holes) that result from volcanoes. The porous material is full of bubbles that appear to result from gases present when the diamonds formed. Conventional diamonds, formed deep within the earth, where the high pressure does not allow gases to exist.
Second, black diamonds are not found in conventional diamond mining locations. Black diamonds are found in Brazil and the Central African Republic but not one has been discovered in Russia, Australia, Canada, or other African countries that are the primary sources of the 600 tons of conventional diamonds that have been mined over the last century. Since conventional diamonds are formed deep in the earth’s crust, geologists have been challenged to explain why black diamond sources are so isolated and separate from conventional diamond locations. Black diamonds are found in alluvial deposits where rivers have washed the stones until they collect in low-lying pockets where they are mined today. Unlike conventional diamonds, the black variety is not found in kimberlite pipes that would indicate they were formed beneath the earth’s crust.
In recent months, a team of geologists led by Stephen Haggerty of Florida International University in Miami presented the results of a study that theorizes that black diamonds came from outer space. The team proposes that an asteroid about half mile in diameter impacted earth billions of years ago where South America and Africa were once connected land masses. Today the deposits of black diamonds are thousands of miles apart because the landmasses drifted apart.
Black diamonds are seldom used as gemstones because they are extremely hard to cut and polish. They seem to have a hardness that exceeds conventional diamonds due to the fact they do not cleave along crystal planes. As a result, regular diamond powder only cuts carbonado with extreme difficulty. This trait makes it ideal for grinding, drilling and other industrial uses but not popular for uses in the jewelry industry.
As the public learns about the possible outer space source of black diamonds, its stellar origin might increase its popularity as a gemstone. Owning a diamond from outer space might be just the marketing theme that changes how diamond shoppers perceive this unique form of diamond.