Scholzite , Cryptomelane Locality: Reaphook Hill, Martins Well station, South Flinders Ranges, Flinders Ranges, South Australia, Australia Description: A 6.8 by 4.6 cms mass of crystals with some black Cryptomelane. JSS specimen and photo. — Photo: John Sobolewski (JSS) · CC BY 3.0
Cryptomelane
The potassium member of the hollandite group — a tunnel-structured manganese oxide common in manganese deposits.
Intro adapted from Wikipedia (CC BY-SA).
Cryptomelane is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula K(Mn⁴⁺₇Mn³⁺)O₁₆.
It crystallizes in the tetragonal crystal system (space group I2/m). It is a member of the Coronadite structural group.
Key properties: Mohs hardness 6–6.5; specific gravity 4.17–4.41; Brownish black streak; Metallic to dull luster.
IMA symbol Cml, IMA status: approved, named in 1942.
Widespread in oxidized manganese deposits as open-space fillings or replacing primary manganese-bearing minerals; commonly replaced by other secondary manganese minerals.
It is found associated with Pyrolusite, nsutite, braunite, chalcophanite, manganite, other manganese oxides.
Its name comes from the Greek for hidden and black, alluding to the mineral’s obscure identity as one of several black mineral species in “psilomelane”, the collective term for hard manganese oxides.