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Download hereGENERAL DESCRIPTION
Arfvedsonite is an hydroxylated iron and sodium silicate. It belongs to the group of amphiboles. It is a mineral which is formed in the alkaline rocks, associated to sodalite and nepheline. Arfvedsonite is often presented in the form of granulous masses, lamellate aggregates and seldomly with more or less flattened prismatic crystals. Arfvedsonite has a green-black to black color and is opaque.
The deposits are very few to display superb crystals. Among them, the Canadian deposits of Mont Saint-Hilaire (prismatic crystals of 20 cm), Ilímaussaq in Greenland (prismatic crystals of 13 cm or more), the Malosa mount in Malawi (well formed crystals of 8 cm). As nepehlinic syenite deposits are rare in France (mostly Fitou in the Pyrénées), there is not deposit of arfvedsonite in continental French which is recognized in the "min.dat" database. Nevertheless, there is a locality in French Polynesia, on the atoll of Mururoa.
The place of conservation of the type of this species (extracted close from Ilímaussaq in Greenland) is not known.
HISTORY : Species dedicated to Johan A. Arfvedson (1792-1841), Swedish chemist
Species described in 1823 by Henry James Brooke (1771–1857), English mineralogist
Type-locality: Compexe de Ilimaussaq, Province de Kitaa, Groënland
ANCIENT NAME : Horneblende ferrifère
CHEMICAL FORMULA : Na3 [(Fe2+;Mg)4 Fe3+] Si8O22 (OH)2
CRYSTAL SYSTEM : Monoclinic
COLOR : Depp green to blueish black
DIAPHANIETY : Transparent to translucent
LUSTER : Vitreous
STREAK : Bright gray to gray-black
MORPHOLOGIE : Elongated crystals, striated. Fibrous radial aggregates
HARDNESS : 5,0-6,0
CHEMICAL CLASS: 3,33
DENSITY : VIII - Silicates
GROUP : Amphibole
STRUNZ CLASS BEFORE 2001 : 8/F.08-100
STRUNZ CLASS AFTER 2001 : 9.DE.25
