Sinoite

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.

Sinoite
Crystal structure of sinoite. Atoms: red – O, blue – N, gray – Si.
General
CategorySilicate mineral
Formula
(repeating unit)
Si2N2O
IMA symbolSno
Strunz classification1.DB.10
Dana classification1.3.9.1
Crystal systemOrthorhombic
Crystal classPyramidal (mm2)
H-M symbol: (mm2)
Space groupCmc21
Unit cella = 8.84 Å, b = 5.47 Å
c = 4.83 Å, Z = 4
Identification
ColorFrom colorless to light gray
CleavageNone
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.83
Optical propertiesBiaxial (-)
Refractive indexnα = 1.740
nβ = 1.855
nγ = 1.855
Birefringenceδ = 0.115
References


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.

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