Epididymite Locality: Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry), Mont Saint-Hilaire , Rouville RCM, Montérégie , Québec , Canada ( Locality at mindat.org ) A superb and complete reticulated epididymite crystal. 2.5 x 2 x 1 cm — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Epididymite
Epididymite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₂Be₂Si₆O₁₅·H₂O.
It crystallizes in the orthorhombic crystal system (space group Pnam).
Key properties: Mohs hardness 5.5; specific gravity 2.55–2.61; Pearly on cleavages, vitreous on fractures luster; optically biaxial.
IMA symbol Edd, grandfathered status — known before the IMA’s founding, named in 1893.
A late-stage mineral in nepheline syenite pegmatites.
It is found associated with Albite, aegirine, eudialyte, elpidite, neptunite, tugtupite, leucophanite, natrolite, analcime.
The prefix epi from the Greek for near, referring to the dimorphous relation with eudidymite.