Diamond
Carbon in its hardest form, found as shock-made crystals in ureilites and as nanodiamonds that may be stardust.
Key facts
- Formula
- C
- Family
- Carbon minerals
- Crystal system
- Cubic
What it is
Diamond is carbon with each atom bonded to four others in a rigid three-dimensional framework, making it the hardest natural mineral. On Earth it forms deep in the mantle; in meteorites it forms in other ways.
Where it is found
Ureilites contain diamonds formed mainly when graphite was shocked by impacts. In 2018 diamonds from the Almahata Sitta ureilite were found to contain inclusions that some scientists interpret as formed under high pressure inside a large parent body, though this is debated.
Primitive chondrites contain nanodiamonds, only about 2 to 3 nanometres across. A few carry xenon with an isotope pattern from supernovae, so at least some are presolar, though most may have formed in the Solar System.
How it is recognised
Ureilite diamonds are tiny and make the rock very hard to cut. Nanodiamonds can only be studied after dissolving the meteorite in acid.
Did you know?
Ureilites are so hard because of their diamonds that they wear out saw blades.
Nanodiamonds were among the first presolar materials found in meteorites, in 1987.