Epididymite

epididymite

bertrandite

chkalovite

elpidite

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Formula: Na₂Be₂Si₆O₁₅.H₂O
Inosilicate (chain silicate), paramorph of eudidymite
Specific gravity: 2.548
Hardness: 5½
Streak: White
Colour: Colourless
Solubility: Insoluble in common acids, soluble in HF (Dana)
Common impurities: Al,Fe,Mg,Ca,K
Environments

Plutonic igneous environments
Pegmatites
Hydrothermal environments

Epididymite occurs in nepheline syenite rocks and their pegmatites as a late hydrothermal mineral. It may form from pre-existing beryllium minerals and may alter to bertrandite and beryllite (Dana, HOM). Associated minerals include albite, aegirine, eudialyte, elpidite, neptunite, tugtupite, leucophanite, natrolite and analcime (HOM).

Localities

At the type locality, the Narssârssuk pegmatite, Narsaarsuk Plateau, Igaliku, Kujalleq, Greenland, Denmark, epididymite occurs as pseudomorphs after chkalovite (Dana).

At Alluaiv Mountain, Lovozersky District, Murmansk Oblast, Russia, At Mt Alluaiv epididymite occurs as pseudomorphs after chkalovite (Dana).

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