A fairly typical eudidymite "fan" from a pegmatite. There are a few small dark green aegirine crystals in the lower right corner. - Locality: Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry), Mont Saint-Hilaire, Rouville RCM, Montérégie, Québec, Canada - FOV 3.1 x 1.8 mm — Photo: Modris Baum · Public domain
Eudidymite
Eudidymite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₂Be₂Si₆O₁₅·H₂O.
It crystallizes in the monoclinic crystal system (space group C2/c).
Key properties: Mohs hardness 6; specific gravity 2.55; Vitreous, pearly on cleavage luster; optically biaxial.
IMA symbol Edy, grandfathered status — known before the IMA’s founding, named in 1887.
A late-stage mineral in alkalic nepheline syenite pegmatites.
It is found associated with Albite, neptunite, aegirine, elpidite, natrolite, analcime, fluorite, quartz.
Its name comes from the Greek for well and twinned, in allusion to its common occurrence in twins.