Tridymite
Chemical Formula	SiO2
Species	Silicates
Crystal System	Triclinic
Mohs Scale	6-7
Specific Gravity	2.25-2.28
Color	Colorless, white
Streak	white
Luster	Vitreous
Refractive Index	n = 1.468 - 1.482 n = 1.470 - 1.484 n = 1.474 - 1.486
Diaphaneity	Transparent, Translucent
Cleavage	Poor/Indistinct Indistinct, Imperfect
Fracture	Conchoidal
Crystal Habit：Platy – sheet forms
Geological Setting：Vapor phase deposition in vesicles and lithophysae, phenocrysts in volcanic rocks, contact metamorphosed sandstones.