Rhomboclase
An acidic hydrated iron sulfate forming rhombic-outlined orthorhombic tablets in acid mine settings.
Intro adapted from Wikipedia (CC BY-SA).
Rhomboclase is an IMA-recognized mineral species in the sulfate class, with the chemical formula (H₅O₂)Fe³⁺(SO₄)₂·2H₂O.
It crystallizes in the orthorhombic crystal system (space group Pnma).
Key properties: Mohs hardness 2; specific gravity 2.23; Subvitreous to pearly luster; optically biaxial.
IMA symbol Rbc, grandfathered status — known before the IMA’s founding, named in 1891.
An uncommon secondary mineral produced through alteration of pyrite, especially in an arid climate; typically of post-mining origin.
It is found associated with Szomolnokite, copiapite, römerite, voltaite, epsomite, halotrichite, melanterite, chalcanthite, pyrite.
Its name comes from the Greek for rhomb, for the typical rhombic crystal outline, and for to break, for its perfect cleavage.