EUCRYPTITE

    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

Eucryptite is always very discreet in its deposits, with the exception of the pegmatite of Bikita (Zimbabwe), where its exceptional abundance makes it an exploited lithium ore. It is present, among other things, in the American pegmatites of Foote (North Carolina), Etta (South Dakota), a deposit famous for its decametric crystals of spodumene, and in the pegmatite of Tanco (Manitoba, Canada). In Europe, eucryptite is found in the pegmatite of Peiräseinäjoki (Finland).

Right photo : Twinned eucryptite from Foote, North Carolina, USA © Jason B. Smith

Eucryptite in France

Eucryptite is not present in the French underground.

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