Grandidierite
Vohibola phlogopite deposit, Behara, Amboasary Sud District, Anosy, Madagascar
2.05 carats
© Jasun McAvoy
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.
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| General Information | ||||||||||||||
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| Chemical Formula |
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| Physical Properties of Grandidierite | ||||||||||||||
| Mohs Hardness | 7.5, Blue Chart Gem Identification (2010) More from other references | |||||||||||||
| Specific Gravity | 2.85 to 3.00, Blue Chart Gem Identification (2010) More from other references | |||||||||||||
| Cleavage Quality | Distinct, Gemmological Tables (2004) More from other references | |||||||||||||
| Fracture | Uneven, Gemstones (2009) | |||||||||||||
| Optical Properties of Grandidierite | ||||||||||||||
| Refractive Index | 1.578 to 1.639, Blue Chart Gem Identification (2010) More from other references | |||||||||||||
| Optical Character | Biaxial/-, Blue Chart Gem Identification (2010) More from other references | |||||||||||||
| Birefringence | 0.037 to 0.039, Blue Chart Gem Identification (2010) DoublingMore from other references | |||||||||||||
| Pleochroism | Distinct: greenish blue - colorless - blue-green, Blue Chart Gem Identification (2010) More from other references | |||||||||||||
| Colour | ||||||||||||||
| Colour (General) | Bluish-green, blue, Gemmological Tables (2004) More from other references | |||||||||||||
| Transparency | Translucent, Gemmological Tables (2004) More from other references | |||||||||||||
| Lustre | Vitreous, Gemstones (2009) | |||||||||||||
| Fluorescence & other light emissions | ||||||||||||||
| Fluorescence (General) | Inert, Blue Chart Gem Identification (2010) | |||||||||||||
| Crystallography of Grandidierite | ||||||||||||||
| Crystal System | Orthorhombic, Blue Chart Gem Identification (2010) More from other references | |||||||||||||
| Habit | Elongated anhedral crystals, Gems, Sixth Edition (2006) More from other references | |||||||||||||
| Geological Environment | ||||||||||||||
| Where found: | Grandidierite occurs in aluminous boron-rich rocks and in pegmatites., 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 | ||||||||||||||
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