Silica minerals: tridymite, cristobalite and quartz
Silicon dioxide in its different crystal forms, found in eucrites, enstatite chondrites and lunar basalts.
Key facts
- Formula
- SiO2
- Family
- Silicates
- Crystal system
- Various
What it is
Silica is silicon dioxide. At low pressure it can take several forms depending on temperature: quartz, the familiar form on Earth; tridymite, stable at higher temperatures; and cristobalite, stable close to melting. At high pressure it becomes coesite, stishovite or seifertite.
Where it is found
Tridymite and cristobalite are the usual silica minerals in meteorites, found in eucrites, mesosiderites, enstatite chondrites and the last parts of lunar and Martian basalts to crystallise. Quartz is rare in meteorites. Silica also forms grains in some chondrules of ordinary and enstatite chondrites.
How it is recognised
It is colourless and usually a minor mineral. Tridymite often forms thin plates, and cristobalite tiles with curved cracks. They are distinguished by X-ray diffraction or Raman spectroscopy.
Did you know?
Abundant quartz in a supposed meteorite is a warning sign that the rock is from Earth.
Tridymite was found by the Curiosity rover in Gale crater, a surprise that suggested past explosive volcanism on Mars.