Sinoite

Sinoite
General
Category	Silicate mineral
Formula (repeating unit)	Si2N2O
Strunz classification	1.DB.10
Dana classification	1.3.9.1
Crystal system	Orthorhombic
Unit cell	a = 8.84 Å, b = 5.47 Å c = 4.83 Å, Z = 4
Identification
Color	From colorless to light gray
Crystal symmetry	Orthorhombic – pyramidal H-M symbol (mm2) Space group: Cmc21
Cleavage	None
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.83
Optical properties	Biaxial (-)
Refractive index	nα = 1.740 nβ = 1.855 nγ = 1.855
Birefringence	δ = 0.115
References	[1][2][3]

Sinoite is rare mineral with the chemical formula Si₂N₂O. It was first found in 1905 in chondrite meteorites and identified as a distinct mineral in 1965. Sinoite crystallizes upon meteorite impact as grains smaller than 0.2 mm surrounded by Fe-Ni alloys and the mineral enstatite. It is named after its SiNO composition and can be prepared in the laboratory as a silicon oxynitride ceramic.^[4]

Crystal structure of sinoite. Atoms: red – O, blue – N, gray – Si.^[5]

The crystalline structure of silicon oxynitride is built by SiN₃O tetrahedra connected through oxygen atoms along the c axis and through nitrogen atoms perpendicular to it. The strong covalent bonding of this structure results in high flexural strength and resistance to heating and oxidation up to temperatures of about 1600 °C.^[6]

References

1. Sinoite. Handbook of Mineralogy
2. Sinoite. Mindat.org
3. Sinoite. Webmineral
4. A. E. Rubin (1997). "Sinoite (Si₂N₂O): Crystallization from EL chondrite impact melts" (PDF). American Mineralogist 82: 1001.
5. Ohashi, Masayoshi; et al. (1993). "Solid Solubility of Aluminum in O'-SiAlON". J. Am. Ceram. Soc. 76 (8): 2112–2114. doi:10.1111/j.1151-2916.1993.tb08343.x.
6. Ralf Riedel (18 April 2008). Ceramics science and technology: Structures. Wiley-VCH. pp. 97–. ISBN 978-3-527-31155-2. Retrieved 8 October 2011.