Spessartine

Spessartine
Spessartine crystals
General
CategoryNesosilicate
Garnet group
Formula
(repeating unit)
Mn2+3Al2(SiO4)3
IMA symbolSps
Strunz classification9.AD.25
Crystal systemIsometric
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupIa3d
Unit cella = 11.63 Å; Z = 8
Identification
ColorYellow through red
Crystal habitMassive to crystalline
CleavageNone
FractureSub-conchoidal
TenacityBrittle
Mohs scale hardness6.5 – 7.5
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity4.19 calculated, 4.12 – 4.32 measured
Optical propertiesIsotropic, often anomalous double refractive
Refractive index1.800
Birefringencenone
DispersionWeak
Absorption spectraBands at 410, 420, 430 nm (or merging to form cutoff below 430 nm; also bands at 460, 480, 520 nm. Possible weak bands at 504 or 573 nm
References

Spessartine is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3. This mineral is sometimes mistakenly referred to as spessartite.

Spessartine's name is a derivative of Spessart in Bavaria, Germany, the type locality of the mineral. It occurs most often in granite pegmatite and allied rock types and in certain low-grade metamorphic phyllites. Sources include Australia, Myanmar, India, Afghanistan, Israel, Madagascar, Namibia, Nigeria, Mozambique, Tanzania and the United States. Spessartine of an orange-yellow has been called Mandarin garnet and is found in Madagascar. Violet-red spessartines are found in rhyolites in Colorado and Maine. In Madagascar, spessartines are exploited either in their bedrock or in alluvium. The orange garnets result from sodium-rich pegmatites. Spessartines are found in bedrock in the highlands in the Sahatany valley. Those in alluvium are generally found in southern Madagascar or in the Maevatanana region.

Spessartine forms a solid solution series with the garnet species almandine. Well-formed crystals from this series, varying in color from very dark-red to bright yellow-orange, were found in Latinka, Rhodope Mountains, Kardzhali Province, Bulgaria. Spessartine, like the other garnets, always occurs as a blend with other species. Gems with high spessartine content tend toward a light orange hue, while almandine prevalence induces red or brownish hues.

Images

See also


This page was last updated at 2024-02-06 05:41 UTC. Update now. View original page.

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