Rhomboclase

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

Rhomboclase
General
Category	Sulfate mineral
Formula	H5Fe3+O2(SO4)2·2(H2O)
IMA symbol	Rbc[1]
Strunz classification	7.CB.55
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnma
Identification
Color	blue, colourless, white, yellow, light green, grey
Luster	sub-Vitreous, Pearly
Streak	white
Diaphaneity	transparent
References	[2][3]

Rhomboclase forms within the oxidizing environment of pyrite rich ore deposits and is reported as a post mine mineral of arid regions.^[4]

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.^[2]