Sillénite

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.[2][3][4]

Sillénite
Sillénite from Germany
General
Category	Oxide mineral
Formula (repeating unit)	Bi12SiO20
IMA symbol	Sén[1]
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	[2][3][4]

Sillenites refer to a class of bismuth compounds with a structure similar to Bi₁₂SiO₂₀, whose parent structure is γ-Bi₂O₃, a meta-stable form of bismuth oxide.[5] The cubic crystal sillenite structure is shared by several synthetic materials including bismuth titanate and bismuth germanate.[6] These compounds have been extensively investigated for their non-linear optical properties.[7][8][9]

Additional stoichiometries, and modified structures, are also found in Bi₂₅GaO₃₉, Bi₂₅FeO₃₉, and Bi₂₅InO₃₉.[10][11] These compounds have gathered recent interest due to their photocatalytic properties.[12]

Recently, sillenites have also gathered interest as heavy metal glass ceramics. They are considered promising materials for laser technology as they combine strong nonlinear properties, relative ease of manufacturing, and low production cost.[13][14]