| Spessartine | |
|---|---|
 Spessartine crystals | |
| General | |
| Category | Nesosilicate Garnet group |
| Formula | Mn2+3Al2(SiO4)3 |
| IMA symbol | Sps [1] |
| 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 [2] |
| References | [3] [4] [5] |
Spessartine is a nesosilicate, manganese aluminium garnet species, Mn2+3Al2(SiO4)3. [2] [3] [4] [5] This mineral is sometimes mistakenly referred to as spessartite. [6]
Contents
Spessartine's name is a derivative of Spessart in Bavaria, Germany, the type locality of the mineral. [3] [4] It occurs most often in granite pegmatite [3] [4] [5] 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. [2] 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. [7] [8] [9] [10] [11]
Spessartine forms a solid solution series with the garnet species almandine. [4] [5] 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. [12] 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. [13]
