Formula: NaFeS2.2H2O
Specific gravity: 2.30
Hardness: 2
Streak: Black
Colour: Copper-red
Solubility: Easily soluble in cold dilute acids with effervescence of H2S. When heated in a closed tube, it gives off water and sulphur and eventually turns black and strongly magnetic (Mindat).
Common impurities: K


Erdite is one of the few sodium-bearing sulphides. It exhibits extreme pleochroism, brilliant reddish orange though greenish greys and pinkish greys to dark grey (Webmin).


At the Alluaiv Mountain, Lovozersky District, Murmansk Oblast, Russia, erdite is found in pegmatites in nepheline syenite associated with pyrite and murmanite (HOM).

At the type locality, Coyote Peak, Coastal Range, Humboldt county, California, USA, erdite is typically associated with other sulphide minerals and magnetite in discrete, late segregations within the mafic, alkalic host rock. Non-sulphide minerals adjacent to and within these segregations include coarse phlogopite and schorlomite crystals, both to 5 mm across, clinopyroxene, nepheline, natrolite, sodalite, vishnevite, aegirine, apatite and barytolamprophyllite. No well-formed crystals of erdite were found. Erdite is typically associated with fine-grained, euhedral magnetite crystals that formed contemporaneously. Pyrrhotite formed first, then djerfisherite and rasvumite and finally erdite and magnetite. Rasvumite replaces pyrrhotite, and erdite replaces djerfisherite (AM 65.509-515)

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