Rhomboclase

Rhomboclase is an acidic iron with a formula reported as H5Fe3+O2(SO4)2·2(H2O) It crystallizes in the orthorhombic system and typically occurs as tabular crystals with a rhombic outline. It occurs as transparent colorless, blue, green, yellow or grey crystals with a vitreous to pearly luster.

Rhomboclase forms within the oxidizing environment of pyrite deposits and is reported as a post mine mineral of arid regions.

It was first described in 1888 for an occurrence in Slovakia and was named from Latin , rhombus, rhomb, and Greek klasis, to break, for its crystal form and perfect basal cleavage.