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|Crystal class||Dipyramidal (mmm) |
H-M symbol: (2/m 2/m 2/m)
|Mohs scale hardness||7.5|
|Optical properties||Biaxial (-)|
|Refractive index||1.583 - 1.639|
|2V angle||Measured: 24° to 32°, Calculated: 32°|
|Dispersion||strong r < v|
Grandidierite, a mineral that was first discovered in 1902 in southern Madagascar. The mineral was named in honor of French explorer Alfred Grandidier (1836–1912) who studied the natural history of Madagascar.
Grandidierite is often touted by commercial parties (eg gemstone mining companies, gem traders- and cutters) as a very rare and expensive gemstone, but with regard to rarity, a clear distinction must be made between pure gem quality and a much more common low quality grandidierite. To be of pure gem quality a stone like grandidierite has to be of high transparency, even color, and with as few internal errors as possible. A much less rare form of grandidierite is one with a low transparency and many internal defects such as fractures and inclusions. This latter form is widely available.
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