| Rhomboclase | |
| Category: | Sulfate mineral |
| Formula: | H5Fe3+O2(SO4)2·2(H2O) |
| Imasymbol: | Rbc[1] |
| Strunz: | 7.CB.55 |
| System: | Orthorhombic |
| Class: | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Symmetry: | Pnma |
| Color: | blue, colourless, white, yellow, light green, grey |
| Luster: | sub-Vitreous, Pearly |
| Streak: | white |
| Diaphaneity: | transparent |
Rhomboclase is an acidic iron sulfate mineral with a formula reported as H5Fe3+O2(SO4)2·2(H2O)[2] or HFe(SO4)2·4(H2O).[3] It crystallizes in the orthorhombic system and typically occurs as tabular crystals with a rhombic outline.[2] It occurs as transparent colorless, blue, green, yellow or grey crystals with a vitreous to pearly luster.[4]
Rhomboclase forms within the oxidizing environment of pyrite rich ore deposits and is reported as a post mine mineral of arid regions.[2]
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.[3]