Kornerupine
Species
Very Rare · (Mg,Fe++,Al,□)₁₀(Si,Al,B)₅O₂₁(OH,F)₂
A boron magnesium silicate of high-grade metamorphic rocks, rare enough that faceted stones are a collector's affair. Green to brown crystals are strongly pleochroic, showing a different colour along each axis, so the cutter must orient the stone.
Identity
- Formula
- (Mg,Fe++,Al,□)₁₀(Si,Al,B)₅O₂₁(OH,F)₂
- Chemical class
- Silicate
- Also known as
- Kornerupite
Crystallography
- Crystal system
- Orthorhombic
- Habits
- Prismatic, Columnar, Fibrous
- Fracture
- Uneven
Physical properties
- Mohs hardness
- 7
- Density
- 3.32 g/cm³
- Luster
- Vitreous
- Colors
- brown, colorless, green, greenish yellow, yellow
- Streak
- white
- Transparency
- Transparent, Translucent, Opaque
Geology
- Origins
- Metamorphic
- Host rocks
- Schist and gneiss
- Associated minerals
- Sillimanite, Kyanite, sapphirine, Iolite
- Geography
- Madagascar, Sri Lanka, Tanzania
Classification
- Rarity
- Very Rare
- Gem quality
- Yes
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.
- Kornerupine. Mindat.org (Hudson Institute of Mineralogy).
- Kornerupine. Mineralogical Society of America, Handbook of Mineralogy, 2021.
Browse the Crystal Encyclopedia — MGS Toolbox