Spessartine
| Spessartine | |
|---|---|
Spessartine crystals on larger quartz crystals from China
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|
| General | |
| Category |
Nesosilicate Garnet group |
|
Formula (repeating unit) |
Mn2+3Al2(SiO4)3 |
| Strunz classification | 9.AD.25 |
| Crystal system | Isometric |
| Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m) |
| Space group | Ia3d |
| Unit cell | a = 11.63 Å; Z = 8 |
| Identification | |
| Color | Yellow through red |
| Crystal habit | Massive to crystalline |
| Cleavage | None |
| Fracture | Sub-conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 6.5 – 7.5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 4.19 calculated, 4.12 – 4.32 measured |
| Optical properties | Isotropic, often anomalous double refractive |
| Refractive index | 1.800 |
| Birefringence | none |
| Dispersion | Weak |
| Absorption spectra | Bands 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, sometimes mistakenly referred to as spessartite, is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3. The mineral spessartine should not be confused with a type of igneous rock (a lamprophyre) called 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, 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.
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Wikipedia