Out Of Stock Tridymite and cristobalite are silica polymorphs that are found principally in siliceous volcanic rocks. The "snowflakes" in snowflake obsidian are bundles of cristobalite crystals. -tridymite and -cristobalite both have structures based on layers of SiO tetrahedra with the 4 individual tetrahera alternately pointing up and down. These layers are stacked so that the upward pointing tetrahedra from one layer share oxygen atoms with the downward pointing tetrahedra in the layer above. Product Numbers SBPS50 (50mm) and SBPS100 (100mm). To check pricing or place your order online, click the *Continue* link. Information on how to place your order by fax or by telephone.