Eucryptite - Encyclopedia
Class : Silicates
Subclass : Nesosilicates
Crystal system : Trigonal
Chemistry : LiAlSiO4
Rarity : Rare
Eucryptite is a rare lithium and aluminum nesosilicate of lithiniferous pegmatites, in which it notably accompanies albite and other lithium minerals (spodumene, lepidolite, etc...). It is the silica-deficient equivalent of spodumene. Its name comes from the Greek eu (good) and kruptos (hide), because it is most often found embedded in albite. Eucryptite occurs in crystalline masses or aggregates, rarely in automorphic crystals measuring up to 3 cm, colorless, white, sometimes brownish. It is exceptionally exploited as lithium ore.
Main photo : Eucryptite from Foote, North Carolina, USA © Chris Emproto
Eucryptite in the World
Right photo : Twinned eucryptite from Foote, North Carolina, USA © Jason B. Smith
Twinning
Some eucryptite samples show polysynthetic twins with alternating thin and wide twin lamellae.
Fakes and treatments
No fake listed for this mineral species.
Hardness : 6.5
Density : 2,65
Fracture : Irregular to conchoidal
Streak : White
TP : Translucent to transparent
RI : 1.570 to 1.587
Birefringence : 0.013
Optical character : Uniaxial +
Pleochroism : None
Fluorescence : Red
Solubility : Acids
Magnetism : None
Radioactivity : None