Grandidierite

Grandidierite is named after Alfred Grandidier, French explorer of Madagascar, specialist of its geography and natural history.

Grandidierite forms characteristic translucent bluish green or greenish blue elongated crystals. It has strong pleochroism: dark blue-green, colourless and dark green.

Crystals up to 8 cm in length and limited amounts of facet-grade rough are found in southern Madagascar.

Grandidierite 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
(Mg,Fe)Al
 
3
(BO
 
4
)(SiO
 
4
)O
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 Grandidierite
Mohs Hardness7.5
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Specific Gravity2.85 to 3.00
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Cleavage QualityDistinct
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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FractureUneven
Arthur Thomas, Gemstones (2009)
Optical Properties of Grandidierite
Refractive Index1.578 to 1.639
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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Birefringence0.037 to 0.039
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) DoublingMore from other references
PleochroismDistinct: greenish blue - colorless - blue-green
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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Colour
Colour (General)Bluish-green, blue
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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TransparencyTranslucent
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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LustreVitreous
Arthur Thomas, Gemstones (2009)
Fluorescence & other light emissions
Fluorescence (General)Inert
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Crystallography of Grandidierite
Crystal SystemOrthorhombic
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
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HabitElongated anhedral crystals
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Geological Environment
Where found:Grandidierite occurs in aluminous boron-rich rocks and in pegmatites.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Inclusions in Grandidierite
Needle-like channels, parallel growth planes - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 6
Further Information
Mineral information:Grandidierite information at mindat.org
Significant Gem Localities
Madagascar
 
  • Anosy
    • Taolañaro (Fort Dauphin)
      • Andranobory
Gems, Sixth Edition, Michael O’Donoghue, 2006, p.414
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