Bílinite
An iron sulfate hydrate produced when pyrite oxidizes in water — highly acidic and associated with acid mine drainage.
Intro adapted from Wikipedia (CC BY-SA).
Bílinite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Fe²⁺Fe³⁺₂(SO₄)₄·22H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c). It is a member of the Halotrichite structural group.
Key properties: Mohs hardness 2; specific gravity 1.88–1.99; Silky luster; optically biaxial.
IMA symbol Bli, grandfathered status — known before the IMA’s founding, named in 1913.
An alteration of iron sulfide in lignite (Světec, Czech Republic); a post-mine mineral with other iron sulfates (Nikitov deposits, Ukraine).
It is found associated with Melanterite (Nikitov deposits, Ukraine).
The name refers to its first-noted occurrence near Bı́lina, Czech Republic.