The Largest Black Diamond Ever Found

Sergio is the largest carbonado and the largest rough diamond ever found. It weighs 3167 carats and was found in the State of Bahia in Brazil in 1895. Like other carbonados it is believed to be of meteoritic origin.

Black diamonds are considered fancy colored diamonds and are graded differently than the more common white or colorless diamonds. 

The origin of the diamond is uncertain, but it is believed to either be the result of a meteoric impact or part of an asteroid that crashed on Earth.

The Largest Black Diamond Ever Found

By meteorite or mantle

As diamonds crystallize in the immense pressures deep within Earth, they occasionally encapsulate minerals from the planet's mantle, such as deep red garnet or green olivine. But these minerals are absent in carbonados. Instead, geologists have found an exotic array of metals, such as the titanium nitride mineral osbornite, which is most commonly found in meteorites.

Perhaps the diamonds formed on carbon-rich stars or planets, bits of which were carried to Earth in meteorites during a period between 4 and 3.8 billion years ago when space rocks regularly pelted our planet.

The precise conditions in the mantle that would allow for carbonado formation remain uncertain. One puzzling feature is that all carbonados are filled with holes, like sponges. Most Earth diamonds form at least a hundred miles below the surface in sizzling temperatures and crushing pressures. Pores couldn't survive such conditions.

Other research suggests the pores may be the result of carbonados crystallizing from hot subterranean fluids, or perhaps the cavities were once filled with minerals that have long since washed away. The cavities may have once contained phosphate minerals enriched in radioactive elements, which could have damaged the diamonds' crystal lattice structure and darkened the diamonds' color as they decayed.

The interconnected networks of pores, however, make it difficult to study any remaining material, since it's not easy to tell whether inclusions are original or minerals that formed later in the diamond's life.

How Do Black Diamonds Get Their Color? 

Black diamonds are different from other coloured rocks because they do not get their shade from chemical impurities, such as nitrogen, hydrogen or boron. Rather, black diamonds owe their colour to numerous dark inclusions (mostly graphite), and their opaqueness is caused by a “polycrystalline” structure that inhibits the reflection of light.