Sillenite

Sillénite
Sillénite from Germany
General
Category	Oxide mineral
Formula (repeating unit)	Bi12SiO20
Strunz classification	4.CB.70
Dana classification	16a.03.05.01
Crystal system	Cubic
Crystal class	Tetartoidal (23) H-M symbol: (23)
Space group	I23
Unit cell	a = 10.110 Å, Z = 2
Identification
Color	Olive-green, gray-green, yellow-green, yellow, reddish-brown
Crystal habit	Cubic crystals
Mohs scale hardness	1–2
Luster	Adamantine
Diaphaneity	Translucent
Specific gravity	9.16
Optical properties	Isotropic
Refractive index	>2.5
Birefringence	none
Solubility	Soluble in hydrochloric acid
References

Sillénite or sillenite is a mineral with the chemical formula Bi₁₂SiO₂₀. It is named after the Swedish chemist Lars Gunnar Sillén, who mostly studied bismuth-oxygen compounds. It is found in Australia, Europe, China, Japan, Mexico and Mozambique, typically in association with bismutite.

The cubic crystal structure of sillénite is shared by several synthetic materials including bismuth silicon oxide, bismuth titanate and bismuth germanate.