Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 [CC-BY-SA-3.0], via Wikimedia Commons
Faceted staurolites are extremely rare and always small and dark in color. Staurolite forms very interesting crystals, but cut gems are too dark to be attractive and lack fire. Nonetheless they are true rarities and prized for their scarcity. Zincian staurolite, though very rare, is lighter in color and more attractive as a cut gem; S.G. 3.79, indices 1.721—1.731; trichroic: green/red/yellow. May be red-brown in incandescent light, yellow-green in daylight. Lusakite is a deep blue, strongly pleochroic cobaltian staurolite from Lusaka, Zambia.
Staurolite Value
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Staurolite Information
| Data | Value |
| Name | Staurolite |
| Crystallography | Monoclinic (pseudo-orthorhombic). Crystals prismatic, typically twinned at 60° or 90°, the latter termed fairy crosses; massive. |
| Colors | Dark brown, reddish brown, yellowish brown, brownish black. |
| Luster | Vitreous to resinous. |
| Hardness | 7-7.5. |
| Density | 3.65-3.83. |
| Birefringence | 0.011—0.015. |
| Cleavage | Distinct 1 direction. Fracture conchoidal. Brittle. |
| Dispersion | 0.023. |
| Stone Sizes | Staurolite is almost never transparent, but if it is, it is then very dark. Cut stones are always tiny, less than 2 carats in general, faceted from Brazilian or Swiss crystals. Smithsonian Institution (Washington, D.C): 3.0 (dark brown. Brazil). |
| Luminescence | None. |
| Spectral | Not diagnostic. Weak band at 5780, strong at 4490. Zincian staurolite; strong broad bands at 6100 and 6320, weaker narrow bands at 5315; spectrum absorbed beyond 4900. |
| Formula | (Fe,Mg,Zn)2Al9Si4O23(OH) + Zn or + Co. |
| Pleochroism | Distinct: colorless/yellow or red/ golden yellow. |
Optics: a =1.739-1.747;β= 1.745-1.753; γ=1.752-1.761.
Biaxial (+), 2V =1 82—90°.
lndices increase with iron content.
Occurrence: Staurolite is a mineral of metamorphic rocks, such as schists and gneiss.
New Hampshire; Maine; Vermont; Connecticut.
Canada; France; USSR; Zambia; Scotland.
Virginia, North Carolina, Georgia: abundant fairy crosses and twinned crystals.
New Mexico; fine twinned crystals.
Brazil: facetable crystals rarely found.
Switzerland: occasionally a facetable crystal is encountered in schists.
Lusaka, Zambia: Lusakite.
Comments: Faceted staurolites are extremely rare and always small and dark in color. Staurolite forms very interesting crystals, but cut gems are too dark to be attractive and lack fire. Nonetheless they are true rarities and prized for their scarcity. Zincian staurolite, though very rare, is lighter in color and more attractive as a cut gem; S.G. 3.79, indices 1.721—1.731; trichroic: green/red/yellow. May be red-brown in incandescent light, yellow-green in daylight. Lusakite is a deep blue, strongly pleochroic cobaltian staurolite from Lusaka, Zambia.
Name: From the Greek stauros + lithos, meaning stone cross.
