Best viewed using Adobe Flash Player (8 or higher).
Download hereGENERAL DESCRIPTION
Sellaite is a rare magnesium fluoride. When crystallized, it is presented as small acicular or lamellate prisms, but generally it is present as fibrous aggregates. It is colourless to translucent, with a pearly luster.
Its origin can be hydrothermal or evaporitic. One also can found it in limestone enclaves, ejected by the Vesuvius volcano (Italy) and as fumerolian deposits (Etna) associated to fluorite. The most beautiful crystals measuring up to 5 cm, were found in the Brumado mine, Bahia, Brazil. They were found in a metamorphic magnesite deposit. Sellaite can be associated with fluorite, sulphur, anhydrite or with gypsum.
In France, it is present in the anhydrites of the Gébroulaz glacier moraine (type locality, close of Moutiers in Savoie, French Alps) and the Fonsante fluorite mine, in the Estérel massif in the Var (hydrothermal).
The place of conservation of the type of this new species published in 1868 (on a sample of Savoy) is not known.
HISTORY : Species dedicated to Quintino Sella (1827-1884), Italian mining engineer and mineralogist
Species described in 1868 by Giovanni Strüver (1842-1915), Italian mineralogist
Type-locality : Glacier of the Gébroulaz, Val Thorens, Savoie, France
CHEMICAL FORMULA : MgF2
CRYSTAL SYSTEM : Tetragonal
COLOR : Colorless to white
DIAPHANIETY : Transparent
LUSTER : Vitreous
STREAK : White
MORPHOLOGIE : Acicular crystals, prismatic, lamellar, forming aggregates, massive
HARDNESS : 5,0-5,5
CHEMICAL CLASS: 3,08
DENSITY : III - Halogenides
GROUP : Sellaite
STRUNZ CLASS BEFORE 2001 : 3/A.06-10
STRUNZ CLASS AFTER 2001 : 3.AB.15
