Tridymite

Description

A naturally occurring vitreous phase of pure Silica. Tridymite is found as small crystals in siliceous volcanic rocks. It is not as common as quartz, but quartz will convert to tridymite at 870C with a 16.2% increase in volume.

Physical and Chemical Properties

Soluble in boiling Sodium carbonate solution

Composition	SiO2
Mohs Hardness	7
Density	2.28-2.30 g/ml