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 of Grandidierite shown against the ten reference minerals, from talc (1) to diamond (10).

Mohs	Reference mineral	Grandidierite
1	Talc
2	Gypsum
3	Calcite
4	Fluorite
5	Apatite
6	Orthoclase
7	Quartz
8	Topaz
9	Corundum
10	Diamond

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

Links may earn a commission at no extra cost to you.

About Grandidierite

A grandidierite é um silicato de magnésio, alumínio e boro extremamente raro, com uma cor azul-verde a verde-azulada característica. É fortemente pleocróica, mostrando três cores diferentes (azul-verde, incolor e azul escuro) conforme a orientação. Descoberta em 1902 em Madagáscar, continua a ser uma das gemas mais raras e menos conhecidas do mundo. Os exemplares transparentes de qualidade gema são muito valorizados por colecionadores. O Sri Lanka e Madagáscar são as principais fontes.

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