Staurolite

Big Photo

Brazil
0.72 carats
© Rarestone.com

Staurolite is named from Greek "stauros" - a cross, alluding to the cruciform twins (fairy crosses) it displays in some cases.

Staurolite forms characteristic monoclinic, pseudo-orthorhombic prismatic, reddish brown crystals, often forming 60° twins. The crystals are mostly translucent, rarely transparent. Staurolite shows distinct pleochroism - colourless - yellow - reddish brown.

Rouch material to facet brilliant gems is very rare.

Staurolite Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 
General Information
Chemical Formula
(Fe,Mg,Zn)
 
2
Al
 
9
(Si,Al)
 
4
O
 
22
(OH)
 
2
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Photos of natural/un-cut material from mindat.org
Physical Properties of Staurolite
Mohs Hardness7 to 7.5
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Specific Gravity3.7 to 3.8
Walter Schumann, Gemstones of the world (2001)
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Cleavage QualityDistinct
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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FractureSub-Conchoidal
Arthur Thomas, Gemstones (2009)
Optical Properties of Staurolite
Refractive Index1.736 to 1.762
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Optical CharacterBiaxial/+
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Birefringence0.010 to 0.015
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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PleochroismDistinct: light yellow - yellowish red - dark red
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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DispersionNil
Arthur Thomas, Gemstones (2009)
Colour
Colour (General)Reddish-brown, black.
Walter Schumann, Gemstones of the world (2001)
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Causes of ColourBrown, Fe2+ in tetrahedral coordination. Blue, Co2+ in tetrahedral coordination
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyTransparent
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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LustreVitreous
Walter Schumann, Gemstones of the world (2001)
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Crystallography of Staurolite
Crystal SystemMonoclinic
Walter Schumann, Gemstones of the world (2001)
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HabitPseudo-orthorhombic prismatic
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Geological Environment
Where found:Staurolite occurs most commonly in schists and gneisses.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Further Information
Mineral information:Staurolite information at mindat.org
Significant Gem Localities
Brazil
 
  • Minas Gerais
    • Rubelita
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 455
Sri Lanka
 
  • Sabaragamuwa Province
    • Ratnapura District
      • Ratnapura
Switzerland
 
  • Ticino
    • Leventina
      • Chironico Valley
Gems, Sixth Edition, Michael O’Donoghue, 2006, p. 455
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