Icosahedrite
The first natural quasicrystal: an aluminium–copper–iron alloy found in the Khatyrka meteorite.
Key facts
- Formula
- Al63Cu24Fe13
- Family
- Metals and alloys
- Crystal system
- Icosahedral (a quasicrystal)
- First described
- the Khatyrka meteorite, 2011
Icosahedrite was described in 2011 from grains of the Khatyrka meteorite, found in the Koryak Mountains of Chukotka in far eastern Russia. It is named after the icosahedron, the twenty-faced solid whose symmetry it shares. It was the first natural quasicrystal ever found.
What it is
A quasicrystal is a solid whose atoms are perfectly ordered but never repeat in a regular pattern. It can show fivefold symmetry, which ordinary crystals cannot have. Quasicrystals were first made in a laboratory in 1982, and for years many scientists doubted that any could form in nature. Icosahedrite proved that they can.
Where it is found
It occurs as tiny grains with other aluminium–copper alloys, olivine, spinel and diopside in the Khatyrka meteorite, a CV3 carbonaceous chondrite. Oxygen isotopes in the silicates, and high-pressure minerals in the grains, showed that the material came from space and that the alloys formed in a collision in the asteroid belt.
How it is recognised
It is identified by electron diffraction, which shows its forbidden tenfold symmetry pattern, and by its unusual composition of metallic aluminium and copper.
Did you know?
The first grain was found in 2009 in a museum sample in Florence, after a decade-long search through rock collections.
An expedition to the Koryak Mountains in 2011 dug up more meteorite grains from clay about 7,000 years old.