GRANDIDIERITE: Madagascar (1.1)
Grandidierite is a rather rare mineral, with a lovely blue-green color. It is never transparent enough to facet, but attractive, sometimes even jadelike cabochons are cuttable from the translucent material. The high hardness makes it suitable for wear, although cutters have to pay close attention to the cleavage. Cut grandidierite is seldom seen in collections because few collectors have even heard of it or know it exists in cuttable form.
Grandidierite Value
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Grandidierite Information
| Data | Value |
| Name | Grandidierite |
| Crystallography | Orthorhombic. Crystals elongated and not well formed; massive. |
| Colors | Blue-green; translucent. |
| Luster | Vitreous |
| Hardness | 7.5 |
| Density | 2.85-3.0 |
| Birefringence | 0.039 |
| Cleavage | Perfect 1 direction, good 1 direction. |
| Stone Sizes | Cut as cabochons up to about 1 inch (1-10 carats). At best, the material is translucent, and generally is opaque. |
| Luminescence | None. |
| Spectral | Not diagnostic. |
| Formula | (Mg,Fe)Al3BSiO9. |
| Pleochroism | Strong: dark blue-green/colorless/ dark green. |
Optics: a = 1.583-1.602; β=1.618-1.636; γ=1.622-1.639.
Biaxial (-), 2V= 30°.
(Madagascar stone: a = 1.583; γ= 1.622; S.G. = 2.85).
Occurrence: Generally in pegmatites.
Andrahomana, South Madagascar: only well-known locality.
Comments: Grandidierite is a rather rare mineral, with a lovely blue-green color. It is never transparent enough to facet, but attractive, sometimes even jadelike cabochons are cuttable from the translucent material. The high hardness makes it suitable for wear, although cutters have to pay close attention to the cleavage. Cut grandidierite is seldom seen in collections because few collectors have even heard of it or know it exists in cuttable form.
Name: After Alfred Grandidier, a French explorer, who described the natural history and geography of Madagascar.
