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Download hereGENERAL DESCRIPTION
Grossular is a aluminocalcic silicate of the garnets family. Natural garnets constitute a family of silicates of relatively simple composition but whose chemical composition varies largely between many end-members. Grossular can be found in limestones having undergone a regional metamorphism or a contact metamorphism (in skarns).
Grossular forms dodecaedric crystals being able to reach 15 cm in length. It presents, outside colourless crystals, a whole range of colours ranging from green (tsavorite variety), yellow, pink (rosolite variety), orange-red (hessonite variety), brown... It can react to UV light (long and short waves) by giving a yellow fluorescence.
Grossular is known in many deposits but the remarkable samples come from Russia (Chernyshevsk), the Val d’Ala (Italy), Zillertal, (Austria), Asbestos (Quebec), Crestmore (California) and Chihuahua (Mexico). The tsavorite variety was only discovered in the years 1960 in Kenya (Merelani, Arusha).
In France, one knows grossular in Framont and Raon l’Etape (Vosges), in Penestin and Lesneven (Brittany), Diélette (Normandy), Canari (Corsica), Bessines-on-Gartempe (Massif Central), Anglade, Costabonne and Arbizon-Saint Lary (the Pyrénées), Pacaudière and Claveisolles (Rhône-Alpes).
14 samples are present in the collections of Bergwerk Akademie ("School of Mines") of Freiberg in Germany.
HISTORY : Name inspired from the Latin " Ribes Grossularia" or gooseberry tree, in reference to its color
Species first described in 1811 by Abraham Gottlob Werner (1749-1817), German geologist
Type-locality: Akhtaragda river, Vilyui basin, Yakoutia, Siberia, Russia
CHEMICAL FORMULA : Ca3 Al2 (SiO4)3
CRYSTAL SYSTEM : Cubic
COLOR : Yellow green to dark green, yellow, colorless, brown
DIAPHANIETY : Transparent to opaque
LUSTER : Vitreous to resineous
STREAK : White
MORPHOLOGIE : Dodecahedric crystals, trapezohedric, hexaoctahedric
HARDNESS : 6,5-7,0
CHEMICAL CLASS: 3,594
DENSITY : VIII - Silicates
GROUP : Garnet
STRUNZ CLASS BEFORE 2001 : 8/A.08-70
STRUNZ CLASS AFTER 2001 : 9.AD.15
