Mallardite
Mallardite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Mn(SO₄)·7H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c). It is a member of the Melanterite structural group.
Key properties: Mohs hardness 2; specific gravity 1.846; White streak; Vitreous luster; optically biaxial.
IMA symbol Mal, grandfathered status — known before the IMA’s founding, named in 1879.
A rare mineral produced through oxidation of Fe–Mn sulfides and carbonates under conditions of saturated relative humidity; typically post-mine, when it may be seasonal.
It is found associated with Manganoan melanterite (Lucky Boy mine, Utah, USA); jokokuite, ilesite, rhodochrosite, manganoan calcite, kutnohorite (Jokoku mine, Japan).
The mineral was named to honor François Ernest Mallard (1833–1894), French crystallographer, National School of Mines, Paris, France.