ELPIDITE

    Class : Silicates
    Subclass : Inosilicates
    Crystal system : Orthorhombic
    Chemistry : Na2ZrSi6O15 3H2O
    Rarity : Rare

Elpidite is a rare sodium and zirconium silicate of alkaline rocks deficient in silica : albitized nepheline syenites, syenitic pegmatites, and fenites in particular. Its name comes from the Greek elpidos (to hope), in the hope of finding other interesting minerals at its place of discovery. It forms prismatic crystals, sometimes decimetric, and flabelliform or fibrous aggregates. Elpidite is colorless or variously colored pale green, green-yellow, brownish, sometimes brick red.

Main photo : Elpidite from Mont St-Hilaire, Quebec, Canada

Elpidite from Mont St-Hilaire, Quebec, Canada
10 cm elpidite from Mont St-Hilaire, Quebec, Canada
Elpidite from Poudrette quarry, Mont St-Hilaire, Quebec, Canada © Modris Baum
Elpidite de Narssârssuk pegmatite, Igaliku, Kujalleq, Greenland ©  OT. Ljøstad

Elpidite in the World

The largest known crystals of elpidite reach 30 cm and come from the alkaline pegmatite of Tarbagatay in Kazakhstan. Superb crystals were also extracted from the Ilimaussaq alkaline syenite complex, near Narssaq (Greenland), and from the nepheline syenites of Lovozero (Kola, Russia), which yielded 6 cm crystals. The alkaline massif of Mont St-Hilaire (Canada) contains crystals up to 10 cm commonly serandite pseudomorphs, counting among the best crystals in the world.

Elpidite in France

In France, elpidite is reported in the alkaline granites of Evisa-Calasima (Southern Corsica).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake listed for this mineral species.


Hardness : 5
Density : 2.52 to 2.62
Fracture : Irregular
Streak : White

TP : Opaque to transparent
RI : 1.560 to 1.574
Birefringence : 0.014
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : -


Magnetism : None
Radioactivity : None