Elpidite Locality: Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry), Mont Saint-Hilaire , Rouville RCM, Montérégie , Québec , Canada ( Locality at mindat.org ) Size: 5.5 x 4.3 x 3.5 cm. This is a very rich specimen of the relatively rare hydrated sodium zirconium silicate Elpidite, seen here in a specimen from the prolific Mont Saint - Hilaire locality. They are often seen in single sprays without matrix, but these sprays do occur on matrix and are remarkably well-defined with individual blades up to 2 cm long. Ex. Martin Lewadny Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Elpidite
Elpidite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₂ZrSi₆O₁₅·3H₂O.
It crystallizes in the orthorhombic crystal system (space group Pbcm).
Key properties: Mohs hardness 5; specific gravity 2.52–2.62; Silky, vitreous to waxy or dull luster; optically biaxial.
IMA symbol Epd, grandfathered status — known before the IMA’s founding, named in 1894.
Found in albitized nepheline syenite and associated pegmatites, aegirine-rich granite, and fenites, in a differentiated alkalic massif (Lovozero massif, Russia).
It is found associated with Albite, quartz, aegirine, epididymite, labuntsovite (Lovozero massif, Russia).
Its name comes from the Greek hope, named in anticipation of discovery of other interesting minerals.