Kornerupine

Real mineral · very rare · (Mg,Fe++)₄Al₆(SiO₄,BO₄)₅(O,OH)₂

A boron magnesium silicate of high-grade metamorphic rocks, rare enough that faceted stones are a collector's affair. Green to brown crystals shift colour between daylight and lamplight along different axes.

Identity

Formula

(Mg,Fe++)₄Al₆(SiO₄,BO₄)₅(O,OH)₂

Chemical class

silicate

Also known as

Prismatine

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

translucent, opaque

Geology

Origins

metamorphic

Host rocks

gneiss, granulite

Associated minerals

Sillimanite, Kyanite, Garnet

Geography

Madagascar, Sri Lanka, Tanzania

Classification

Rarity

very rare

Gem quality

Yes

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