Natural Quasicrystals

Quasicrystals are solids whose atomic arrangements have symmetries forbidden for periodic crystals, including configurations with five-fold symmetry. All examples identified to date have been synthesized in the laboratory under controlled conditions. Here we present evidence of a naturally-occurring icosahedral quasicrystal that includes six distinct five-fold symmetry axes. Icosahedrite, an alloy of aluminum, copper and iron, occurs as micron-sized grains associated with crystalline khatyrkite and cupalite in samples from the Koryak mountains in Russia. The existence of Icosahedrite demonstrates that quasicrystals can form and remain stable under geologic conditions, thereby expanding significantly the types of structures now known to form naturally.