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 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.