Szomolnokite
The iron end-member of the kieserite series — a yellow-brown iron sulfate named for Szomolnok, Slovakia.
Intro adapted from Wikipedia (CC BY-SA).
Szomolnokite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Fe(SO₄)·H₂O.
It crystallizes in the monoclinic crystal system (space group C2/c). It is a member of the Kieserite structural group.
Key properties: Mohs hardness 2.5; specific gravity 3.03–3.07; Vitreous luster; optically biaxial.
IMA symbol Szo, grandfathered status — known before the IMA’s founding, named in 1891.
An uncommon secondary mineral formed in pyrite-rich oxidized sulfide deposits, typically under highly acid and arid conditions.
It is found associated with Rhomboclase, halotrichite, fibroferrite, römerite, copiapite, voltaite, pyrite.
The name refers to the first recognized occurrence at Szomolnok, Hungary (now Smolnı́k, Slovakia).