Orange brown acicular crystals of the very rare mineral erdite. The mineral is one of the few sulphides with sodium in its composition known (NaFeS2 · 2H2O), and has only been found in 4 localities worldwide. From: Coyote Peak, Coastal Range, Humboldt County, California, United States of America. — Photo: David Hospital · CC BY-SA 4.0
Erdite
Erdite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula NaFeS₂·2H₂O.
It crystallizes in the monoclinic crystal system (space group C2/c).
Key properties: specific gravity 2.2; Black streak.
IMA symbol Erd, IMA status: approved, named in 1977.
Found in abundance, typically in association with other sulfides and fine grained magnetite, in discrete, late segregations within an alkalic mafic diatreme (Coyote Peak, California, USA).
It is found associated with Pyrrhotite, magnetite, rasvumite, djerfisherite, bartonite (Coyote Peak, California, USA); pyrite, murmanite (Lovozero massif, Russia).
The name refers to Dr. Richard Clarkson Erd (1924–), American mineralogist with the U.S. Geological Survey, who first synthesized the compound.