Carbonado

A massive (polycrystalline), porous, opaque, gray, brown, or black variety of diamond used as an abrasive and in rock drills.

Five different theories for the formation of carbonado have been discussed.
1. Meteoritic impact;
2. Growth and sintering in the crust or mantle;
3. Subduction;
4. Radioactive ion implantation of carbon substrates;
5. Extraterrestrial.

To understand the genesis of carbonado, it is necessary to take into account the following:

1 - The clastic form of its outcrops, indicating that they are fragments of a large geological body;

2 - The high degree of mechanical wear, which, along with the isotopic age, indicates the antiquity of these diamonds: Archean or early Proterozoic;

3 - True carbonados are an endemic variety of diamond, and they are distributed only in territories in Brazil and Central Africa, which, within Gondwana, were united and separated only in the Mesozoic due to the opening of the Atlantic.

The most likely precursor to carbonado is shungite or both carbonado and shungite originated from a similar precursor substance. It corresponds to carbonado in carbon isotope composition, age, and presence of mineral impurities.

See also the varieties bort, ballas.