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Download hereGENERAL DESCRIPTION
Eudidymite is an hydrated beryllium silicate which is found in rare intrusive igneous rocks, enriched in sodium that are called agpaites (nephelite syenites).
The crystals of eudidymite are white or colourless and show a vitreous lustre. Generally of small size, they seldom exceed 5 cm.
The Kola peninsula in Russia, the Mont Saint-Hilaire in Canada, the area of Langesundfjorden in Norway and Narssarssuk in Greenland are some sites where crystals of eudidymite of exceptional size were discovered. No deposits are yet known in France.
The type of this species is kept at the Naturhistoriska Riksmuseet of Stockholm in Sweden (originating from Lille Arøya in Langesundsfjorden, near Larvik, Vestfold area in Norway).
HISTORY : Name inspired from the Greek word "ευ" [eu] meaning good et "διδυμοσ" [didumos] meaning "twins" in reference to its frequent twinneds
Species described in 1887 by Waldemar Christopher Brøgger (1851-1940), Norvegian geologist and mineralogist
Type-locality: Ile d'Aro, Langesundfjorden, Larvik, Norvège
CHEMICAL FORMULA : Na Be Si3O7 (OH)
CRYSTAL SYSTEM : Monoclinic
COLOR : Colorless to white, more scarcely blue, violet
DIAPHANIETY : Transparent to translucent
LUSTER : Vitreous
STREAK : White
MORPHOLOGIE : Tabular crystals up to 5 cm, frequently twinneds, aggregates, massive
HARDNESS : 6
CHEMICAL CLASS: 2,57
DENSITY : VIII - Silicates
GROUP : Epididymite - eudidymite series
STRUNZ CLASS BEFORE 2001 : 8/G.04-10
STRUNZ CLASS AFTER 2001 : 9.DG.35
