Brown crystal aggregates of the rare Fe sulphate mineral ferrohexahydrite from a locality in Poland (Pomorzany Mine, Olkusz, Malopolskie, Poland). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Ferrohexahydrite
Ferrohexahydrite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Fe²⁺(SO₄)·6H₂O.
It is a member of the Hexahydrite structural group.
Key properties: specific gravity 1.934; optically biaxial.
IMA symbol Fhhy, IMA status: approved, named in 1947.
Found in oxidized ore-bearing sandstone (Sofiya mine, Ukraine); a dehydration product of melanterite in drill cores (northeastern Tatarstan, Russia).
It is found associated with Melanterite (northeastern Tatarstan, Russia).
As a ferrous iron sulfate with six essential water molecules per formula unit.