Grandidierite Description

Gem-quality grandidierite is extremely rare, and it often appears on the list of the 10 rarest varieties in the world, along with gems like jeremejevite, painite, benitoite and taafeite. Many rare gem collectors would love to add grandidierite to their collections, but it has been almost impossible to find. The recent discovery of some gem quality material in Madagascar has now made a few high quality stones available. Grandidierite was first discovered in 1902 in Madagascar by Alfred Lacroix, a French mineralogist. Lacroix named the mineral in honor of French explorer and naturalist Alfred Grandidier (1836–1912), the first authority on the natural history of Madagascar. Since its initial discovery, samples of grandidierite have been found in only a few locations around the world, including Malawi, Namibia and Sri Lanka. But the few gem quality specimens have come mainly from Madagascar. Gemologically, grandidierite is a magnesium aluminum borosilicate. It has a hardness of 7 to 7.5 on the Mohs scale, similar to garnet; a density of 2.85 to 3.00, in the approximate range of tourmaline; and a refractive index of 1.590-1.623. It forms in the orthorhombic crystal system. Grandidierite is typically bluish green in color and derives its distinctive color from traces of iron. The hardness of the gem makes attractive fine jewelry, but cutters must be careful when shaping the stone to avoid fractures. Jewel experts typically cannot set a specific price for the gem, but they generally estimate about $20,000 a carat. INFORMATION Color:    Bluish green Twinning:    none Cleavage :  Perfect Fracture:    Brittle scale hardness:  7.5 Luster:    Vitreous, Pearly Streak:    White Diaphaneity:  Transparent, Translucent Density:    2.976 Optical properties:  Biaxial (-) Refractive index:  1.583 - 1.639 Pleochroism:  Visible 2V angleMeasured: 24° to 32°, Calculated: 32° Dispersion:  strong r < v>

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