Burnt amethyst

Category: Mineral variety

Chemical formula: Silica (silicon dioxide, SiO2)

Strunz classification: 04.DA.05

Dana classification: 75.01.03.01

Crystal symmetry: Trigonal 32

Unit cell: a = 4.9133 Å, c = 5.4053 Å; Z=3

Refractive index: nω = 1.543–1.545 nε = 1.552–1.554

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