Spessartine

Spessartine

Spessartine from China
General
Category Nesosilicate
Formula
(repeating unit)		 Mn2+3Al2(SiO4)3
Strunz classification 9.AD.25
Crystal system Isometric
Unit cell a = 11.63 Å; Z = 8
Identification
Color Yellow through red
Crystal habit Massive to crystalline
Crystal symmetry Isometric – hexoctahedral
H-M symbol: (4/m 3 2/m)
Space group: I a3d
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, sometimes mistakenly referred to as spessartite,[5] 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.[6][7][8][9][10]

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.[11] 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.[12]

The mineral spessartite should not be confused with a type of igneous rock (a lamprophyre) called spessartite.

See also

Spessartine crystal on muscovite matrix from Tanzania

References

  1. 1 2 3 Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  2. 1 2 3 4 Webmineral Spessartine page
  3. 1 2 3 4 5 Mindat Spessartine page
  4. 1 2 3 4 Handbook of Mineralogy Spessartine page
  5. ↑ International Mineralogical Association (1971). "International Mineralogical Association: Commission on new minerals and mineral names" (PDF). Mineralogical Magazine 38: 102–105.
  6. ↑ "Gem News". Gems & Gemology 34 (1): 50–63. 1998-04-01. doi:10.5741/GEMS.34.1.50. Retrieved 2012-04-08.
  7. ↑ Shigley, James; Dona Dirlam; Brendan Laurs; Edward Boehm; George Bosshart; William Larson (2000). "Gem localities of the 1990s". Gems & Gemology 36 (4): 292–335. doi:10.5741/GEMS.36.4.292. Retrieved 2012-04-08.
  8. ↑ Laurs, Brendan; Kimberly Knox (2001). "Spessartine garnet from Ramona, San Diego County, California". Gems & Gemology 37 (4): 278–295. doi:10.5741/GEMS.37.4.278. Retrieved 2012-04-08.
  9. ↑ Rossman, George R. (2009). "The geochemistry of gems and its relevance to gemology: different traces, different prices". Elements 5 (3): 159–162. doi:10.2113/gselements.5.3.159. ISSN 1811-5209. Retrieved 2012-04-08.
  10. ↑ Schmetzer, Karl; Thomas Hainschwang; Lore Kiefert; Heinz-Jürgen Bernhardt (2001). "Pink to pinkish orange Malaya garnets from Bekily, Madagascar". Gems & Gemology 37 (4): 296–308. doi:10.5741/GEMS.37.4.296. Retrieved 2012-04-08.
  11. ↑ "Spessartine from Latinka, Bulgaria:".
  12. ↑ Spessartite Garnet Gemological Information
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