Grandidierite

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An exceptionally rare magnesium iron aluminum borosilicate, grandidierite shows a distinctive blue-green to teal color from traces of iron and exhibits strong trichroism in blue, green, and colorless. It was first described in 1902 from southern Madagascar by the mineralogist Alfred Lacroix and named for the explorer Alfred Grandidier, remaining among the scarcest of gem minerals until larger Madagascar deposits appeared in the 2010s. Crystallizing in the orthorhombic system, it measures 7.5 on the Mohs scale, hard enough for jewelry. Transparent faceted grandidierite, a moderately priced semi-precious stone, commands premium prices among collectors for its rarity and striking aqua tone.

Physical & Optical Properties

Category Semi-Precious Gems

Mohs Hardness 7.5

Specific Gravity 2.85 – 3.0

Refractive Index 1.578 – 1.639

Crystal System Orthorhombic

Luster Vitreous

Cleavage Distinct

Fracture Uneven

Color various

Birefringence 0.037

Mohs Hardness

Mohs Hardness: 7.5

1 Soft10 Hard

Crystal System

Value & Market

Price Tier Moderate ($50-500/ct)

Where to Buy Grandidierite

Blue Nile Fine jewelry retailer

James Allen Gemstone jewelry

Brilliant Earth Ethically sourced gems

Amazon Wide selection

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About Grandidierite

Grandidierite is an exceptionally rare magnesium iron aluminum borosilicate, displaying a distinctive blue-green to teal color due to traces of iron and exhibiting strong trichroism in blue, green, and colorless. First described in 1902 from southern Madagascar by French mineralogist Alfred Lacroix and named for explorer Alfred Grandidier, it remained one of the rarest gem minerals until larger deposits were found in Madagascar in the 2010s. Fine transparent faceted grandidierite commands premium prices among collectors for its rarity and striking aqua color.