Stishovite: Thermal Dependence of the Crystal Habit.

The crystal habit of stishovite changes with the temperature of crystallization at a pressure of about 120 kb. Below 600 degrees C it is bipyramidal; between 600 degrees and 900 degrees C it is granular; and above 900 degrees C it is acicular. This temperature dependence of the crystal habit of stishovite may constitute a highpressure geological thermometer which could indicate limiting values for the peak temperatures that prevailed at craters of meteoritic origin in highly siliceous rocks. It suggests that natural acicular stishovite from the rim sandstone at Meteor Crater, Arizona, crystallized at temperatures above 900 degrees C.