Staurolite
| Refractive Index : 1.746 – 1.736 (+0.015 – 0.015) |
| Optical Characteristic : DR, B+, AGG |
| Specific Gravity : 3.71 (+0.08 -0.06) |
| Formula : (Fe++,Mg)2AI9(Si,AI)4O20(O,OH)4 |
| Crystal System : Monoclinic |
| Variety/Species : All |
| Species/Group : staurolite |
| Birefringence : 0.009 to 0.015 |
| Dispersion : 0.021 |
| Hardness : 7 to 7.5 |
| Toughness : fair |
| Ultrasonic : risky |
| Steam : risky |
| UV Long : Inert |
| UV Short : Inert |
| Pleochroism : 3 colors |
| Strength : moderate |
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| Pleochroism Colors : Transparent brown stones: moderate, yellow to red, brownish yellow and colorless. |
| Heat : stable |
| Acids : slightiy attacked by acids |
| Light : stable |
| Polish Luster : vitreous to resinous |
| Fracture : conchoidal, to uneven |
| Fracture Luster : Dull to vitreous |
| Clarity Type : N/A |
| Tones : N/A |
| Saturations : N/A |
| Cause of Color : Iron and titanium |
| Enhancements : Impregnation or wax/plastic coating |
| Cleavage : distinct 1 direction. |
| Color Range : Most often, brown, black. Rarely transparent brown. |
| Transparency : Tranparent to opaque |
| Phenomena : None |
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| Separations : Staurolite from- Chrysoberyl : RI, spectrum, birefringence (possibly) Opaque staurolite twins have a very distinctive cross shaped appearance. |
| Identifying Characteristics and information Twin crystals occur at 90 or 60 degrees to one another. Often left uncut in cross shapes. Zincian staurolite is very rare but lighter in color and more attractive (when faceted) than staurolite. Lusakite (also very rare) is cobaltian staurolite which is adeep blue. It is strongly pleochroic. |
| Spectral Data Strong line near 4500. Weaker line near 5800. Rarely bands at 6100, 6320 and 5320. |
| Trade Names and Misnomers Cross Stones Fairy Cross Lusakite Staurolite Staurotide Zincian Staurolite |
Tags: staurolite
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