Class : Sulfates, chromates, molybdates
    Subclass : Hydrated sulfates
    Crystal system : Orthorhombic
    Chemistry : HFe(SO₄)₂ 4H₂O
    Rarity : Rare

Rhomboclase is an uncommon iron sulfate formed by the alteration of iron sulfides in arid climates. It is part of a classic mineralogical procession to which other iron sulfates belong (copiapite, voltaite, jarosite, amarantite, botryogen, fibroferrite, etc...), resulting like it from precipitation from "natural" sulfuric acid formed by the reaction of surface water with iron sulfides. By changing the environmental conditions (temperature, pH, oxidation-reduction potential), these sulfates are easily hydrolyzed into ferric hydroxides (goethite, limonite). Its name comes from the Greek rhombos (diamond) and klasis (breakage) to emphasize the mineral's belonging to the orthorhombic system as well as its marked basal cleavage. Rhomboclase occurs in thin lamellar to tabular crystals, or in stalactites with a radiated lamellar texture, colorless, white to gray or pale yellowish, sometimes bluish or greenish.

Main photo : Rhomboclase from Lousal Mine, Portugal © Martins da Pedra

No known twinning for this mineral species.

No fakes listed for this mineral species.