Grandidierite
Species
Legendary · (Mg,Fe++)Al₃O₂(BO₃)(SiO₄)
A rare magnesium aluminium borosilicate, and rarer still as a clear gem. First described in 1902 from Andrahomana in southern Madagascar. Its strong trichroism shifts from deep blue-green to colourless to green with the viewing angle. Facetable crystals of any size are extraordinary finds.
Identity
- Formula
- (Mg,Fe++)Al₃O₂(BO₃)(SiO₄)
- Chemical class
- Silicate
Crystallography
- Crystal system
- Orthorhombic
- Habits
- Prismatic, Massive
- Fracture
- Uneven
Physical properties
- Mohs hardness
- 7.5
- Density
- 2.98 g/cm³
- Luster
- Vitreous
- Colors
- blue-green, teal, pale blue
- Streak
- white
- Transparency
- Transparent, Translucent
Geology
- Origins
- Metamorphic
- Host rocks
- Granite, Schist and gneiss
- Associated minerals
- Kornerupine, Corundum, Spinel, sapphirine
- Found in
- Pegmatite deposit
- Geography
- Madagascar, Malawi, Algeria, Canada, Norway
Classification
- Rarity
- Legendary
- Gem quality
- Yes
Arcane properties
- Affinity
- Water, Air
- Effects
- Scrying, Planar travel
- Planar origin
- Material Plane
Sources
- M. Pasero and others, IMA Commission on New Minerals, Nomenclature and Classification, The New IMA List of Minerals, updated September 2026. International Mineralogical Association (CNMNC), 2026.
- J. W. Anthony, R. A. Bideaux, K. W. Bladh, M. C. Nichols, Grandidierite. Mineral Data Publishing, Handbook of Mineralogy, 2001.
- Grandidierite. Wikipédia, l'encyclopédie libre.
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