Ilvaite - Encyclopedia

    Class : Silicates
    Subclass : Sorosilicates
    Crystal system : Orthorhombic
    Chemistry : CaFe3OSi2O7(OH)
    Rarity : Uncommon


The ilvaite is an uncommon mineral of pyrometasomatic iron deposits in contact with limestones or dolomites, in particular many magnetite skarns, and more rarely nepheline syenites and magnetite gabbros. Its name is due to the Island of Elba his locality of discovery. It most often occurs in elongated prismatic crystals strongly striated according to the elongation, and also in shapeless grains, in compact granular masses, sometimes with fibro-radiated textures, or in brown-black columnar aggregates. The ivory is a bright black color with brownish or greenish reflections, evoking tourmaline. It is often "rusty" on the surface. It is a mineral appreciated by collectors.

Ilvaite from Huanggang Mine, Inner Mongolia, China
Ilvaite from Huanggang Mine, Inner Mongolia, China
Ilvaite from Elba Island, Italy (type-locality)
Ilvaite and calcite from Dalnegorsk, Russia

Ilvaite in the World

The Italian pyrometasomatic deposits have provided excellent group of crystals, in particular the Elba Island (Rio Marina) where the crystals reach 2 cm in a skarn in contact with a dolomite. The Greek island of Seriphos in the Cyclades islands, had delivered the largest known crystals (10 cm) before the discovery of the Chinese deposits, but they are often dull. Beautiful black and shiny crystals come from the Laxey mine in Idaho, they crystallize in the cracks of a hedenbergite lens in contact with a marble. The copper mines of the Russian Urals and Dalnegorsk (Eastern Siberia) also produced good crystals. The best crystals in the world remain those of the Huanggang Mine in Inner Mongolia, China. Discovered in late 2009, but still extracted today, they can reach 20 cm, and are perfectly black and shiny. The best deposit of ilvaite in nepheline syenite is located when it is in the south of Greenland (Siorarsiut).

Twinning

Ilvaite has no twinned crystals known.

Fakes and scams

No scam known for this mineral.



Hardness : 5.5 to 6
Density : 3.99 to 4.05
Fracture : Irregular
Trace : Brown



TP : Opaque
RI : 1.727 to 1.883
Birefringence : 0.156
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None


Solubility : Hydrochloric acid

Magnetism : None
Radioactivity : None

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