Coesite
A high-pressure form of silica that marks impacts on Earth and occurs in some shocked meteorites.
Key facts
- Formula
- SiO2
- Family
- High-pressure minerals
- Crystal system
- Monoclinic
What it is
Coesite is silica packed more densely than quartz. It forms at pressures above about 2.5 gigapascals. It was first made in the laboratory in 1953 by Loring Coes, and was found in nature in 1960 at Meteor Crater in Arizona, where it became one of the first proofs that the crater was made by an impact.
Where it is found
It is found in shocked rocks at impact craters such as Meteor Crater and the Nördlinger Ries, and in rocks pushed deep into Earth by plate movements. In meteorites it has been reported in a few strongly shocked lunar and other meteorites.
How it is recognised
It is identified by X-ray diffraction or Raman spectroscopy, usually as tiny grains in shocked quartz.
Did you know?
Coesite helped prove that the Nördlinger Ries in Germany is an impact crater.
It survives at the surface because it changes back to quartz extremely slowly.