Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Monoclinic
    Chemistry : KMn₈O₁₆
    Rarity : Quite common

Cryptomelane is one of the manganiferous products designated under the generic name psilomelane. This is “psilomelane potassium”, potassium can be very partially replaced by other elements, notably thallium. It is found in the superficial parts of rocks and manganiferous deposits. Its name is derived from the Greek kruptos (hidden) and melanos (black) because this mineral was difficult to identify among the other manganese oxides, also black. Cryptomelane rarely forms small automorphic crystals (2 mm maximum), and rather occurs in earthy or compact masses, or in collomorphic botryoidal aggregates, fibrous to fibroradiated, steel gray blue to black, staining the fingers. Like most cryptocrystalline manganese minerals, it tends to evolve into well-crystallized species (pyrolusite, manganite). Its rarity and the poor quality of its crystals make it a mineral that is not very popular with collectors, although it constitutes a significant manganese ore.

Main photo : Cryptomelane de Serra da Mina Mine, Cercal do Alentejo, Santiago do Cacém, Setúbal, Portugal © Martins da Pedra

No twin known for this mineral species.

No fakes listed for this mineral species.