Spessartine
| Spessartine | |
|---|---|
| 240px
Spessartine from China
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| General | |
| Category | Nesosilicate |
| Formula (repeating unit) |
Mn2+3Al2(SiO4)3 |
| Strunz classification | 09.AD.25 |
| Crystal symmetry | Isometric hexoctahedral H-M symbol: (4/m 3 2/m) Space group: I a3d |
| Unit cell | a = 11.63 Å; Z=8 |
| Identification | |
| Color | Yellow through red |
| Crystal habit | Massive to crystalline |
| Crystal system | Isometric |
| 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 [1] |
| References | [2][3][4] |
Spessartine is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3.[1][2][3][4]
The name is a derivative of Spessart in Bavaria, Germany, the type locality of the mineral.[2][3] It occurs most often in granite pegmatite[2][3][4] and allied rock types and in certain low-grade metamorphic phyllites. Sources include Australia, Myanmar, India, Afghanistan, Israel, Madagascar, Tanzania and the United States.[1] 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.[5][6][7][8][9]
Spessartine forms a solid solution series with the garnet species almandine.[3][4] 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.[10] 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.[11]
The mineral spessartite should not be confused with a type of igneous rock (a lamprophyre), which is called spessartite. Spessartine is called spessartite sometimes, a mistake.[12]
See also
- Garnet
- Almandine
- Andradite
- Grossular
- Pyrope
- Tsavorite
- Uvarovite
- Geology
- Mineral collecting
- Mineral
- Gemstone
References
- ↑ 1.0 1.1 1.2 Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
- ↑ 2.0 2.1 2.2 2.3 Webmineral Spessartine page
- ↑ 3.0 3.1 3.2 3.3 3.4 Mindat Spessartine page
- ↑ 4.0 4.1 4.2 4.3 Handbook of Mineralogy Spessartine page
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- ↑ Spessartite Garnet Gemological Information
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