Formula: NaFeS2.2H2O
Sulphide
Crystal System: Monoclinic
Specific gravity: 2.30 measured, 2.216 calculated
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
Environments
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).
Localities
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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