Ranciéite (Size: 2.2 cm x 3.3 cm x 2 cm) Locality: Siresol Mine, Vajo Siresol, Montecchio, Negrar, Verona Province, Veneto, Italy — Photo: Paolo Franchi · Public domain
Ranciéite
Ranciéite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (Ca,Mn²⁺)₀.₂(Mn⁴⁺,Mn³⁺)O₂·0.6H₂O.
It crystallizes in the hexagonal crystal system (space group P-3).
Key properties: specific gravity 3.336; Pale reddish brown with a lilac to purple hue streak; Bright metallic luster.
IMA symbol Rnc, grandfathered status — known before the IMA’s founding, named in 1859.
A product of weathering or alteration of manganese deposits, commonly formed in limestone or in caves in limestone.
It is found associated with Todorokite, calcite, “limonite”.
The name refers to its first-noted occurrence at Rancié, France.