KORNERUPINE

    Class : Silicates
    Subclass : Nesosilicates
    Crystal system : Orthorhombic
    Chemistry : (Mg,Fe)4Al6(Si,Al,B)5O21(OH,F)
    Rarity : Quite common

Kornerupine is a complex boron silicate present in highly metamorphosed aluminous rocks (amphibolite to granulite facies), as well as in metamorphosed anorthosite complexes. It accompanies other minerals symptomatic of intense metamorphism (sapphirine, corundum, cordierite, sillimanite, etc...). Kornerupine forms with or instead of tourmaline if boron is sufficiently abundant ; it can replace or be replaced by grandidierite. It was named in honor of the Danish geologist Andreas Nikolaus Kornerup. Kornerupine occurs in prismatic crystals up to 20 cm, often united in radiated aggregates. Its color is very variable : from colorless to black, with predominance of blue, green and dark brown-green tones. It is quite often cut as a gemstone.

Main photo : Kornerupine from Kyauk-wa, Mogok, Myanmar © Harald Schillhammer

Kornerupine in the World

Kornerupine is not a rare mineral : its deposits are numerous and distributed across all continents. The most beautiful crystals come from Madagascar : Itrongahy, near Betroka, which provided splendid gemmy crystals of a water green color, and Begogo. The Fiskenaesset complex (Greenland) also yielded 23 cm crystals (50 cm crystals are reported from other, unspecified sites in Greenland). It is also known in the Kwale district (Kenya) in gemmy crystals of 10 cm. Kornerupine is also known in beautiful crystals in South Africa (Bokseputs and Port Shepstone), in the Northern Territories in Australia, and near Langesund, in southern Norway. It accompanies zircon, spinel and garnet in the gem-bearing alluvium of Sri Lanka (Matale, Ratnapura, etc...).

Right photo : 1.68 ct kornerupine du Sri Lanka

Kornerupine in France

In France, kornerupine is known in the granulites of Etang de Lers (Ariège).

Twinning

No twins known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 6 to 7
Density : 3.29 to 3.35
Fracture : Undeterminated
Streak : White

TP : Opaque to transparent
RI : 1.660 to 1.684
Birefringence : 0.014
Optical character : Biaxial -
Pleochroism : Low
Fluorescence : None

Solubility : Hydrofluoric acid

Magnetism : NoneRadioactivity : None