Spessartine

Spessartine
Spessartine crystals
General
Category	Nesosilicate Garnet group
Formula (repeating unit)	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]

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]

Images

• 
  Spessartine crystal from Pakistan
• 
  Spessartine on smoky quartz: Wushan Spessartine Mine, Tongbei, Fujian Province, China
• 
  Reddish-orange spessartine
• 
  Two "frog-eyes" of 1.8 cm each sit perched atop a matrix

See also

References

External links

This page was last edited on 27 September 2023, at 07:18