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Category Sulfate mineral
(repeating unit)
Strunz classification 7.CB.55
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnma
Color blue, colourless, white, yellow, light green, grey
Luster sub-Vitreous, Pearly
Streak white
Diaphaneity transparent
References [1][2]

Rhomboclase is an acidic iron sulfate mineral with a formula reported as H5Fe3+O2(SO4)2·2(H2O)[3] or HFe(SO4)2·4(H2O).[1] It crystallizes in the orthorhombic system and typically occurs as tabular crystals with a rhombic outline.[3] It occurs as transparent colorless, blue, green, yellow or grey crystals with a vitreous to pearly luster.[2]

Rhomboclase forms within the oxidizing environment of pyrite rich ore deposits and is reported as a post mine mineral of arid regions.[3]

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.[1]