Tridymite is a high-temperature polymorph of silica and usually occurs as minute tabular white or colorless pseudo-hexagonal crystals, or scales, in cavities in felsic volcanic rocks.

[4][5] However, tridymite does usually not form from pure β-quartz, one needs to add trace amounts of certain compounds to achieve this.

In the table, M, O, H, C, P, L and S stand for monoclinic, orthorhombic, hexagonal, centered, primitive, low (temperature) and superlattice.

[2] In December 2015, the team behind NASA's Mars Science Laboratory announced the discovery of large amounts of tridymite in Marias Pass on the slope of Aeolis Mons, popularly known as Mount Sharp, on the planet Mars.

Following conjunction, NASA directed the Curiosity rover back to the area where the readings had been taken and discovered that large amounts of tridymite were present.