Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Variable
    Chemistry : Mn_xO_y
    Rarity : Quite common to very common

Psilomelane is a general term grouping together hard manganese oxides, indeterminate in their massive form. Its composition is therefore variable to a large extent, admitting high contents of cobalt, lithium, potassium, calcium or barium, and sometimes tungsten. Psilomelane brings together several minerals including romanechite (barytic, the most common of the psilomelanes, to the point that these two terms are sometimes considered synonymous), asbolane (cobaltiferous), ranciéite (calcic), birnessite, lithiophorite and cryptomelane (potassium). Psilomelanes are minerals of colloidal origin, always collomorphic, evolving towards better crystallized species, mainly romanechite. Psilomelanes are very common as a product of surface alteration of most manganese deposits and metalliferous deposits with manganese carbonate matrix, and therefore constitute a significant portion of manganese ores. This term comes from the Greek psilos (smooth) and melanos (black), thus illustrating the appearance of its polycrystalline aggregates. It appears in compact masses, often hilly with a smooth, seemingly amorphous surface, sometimes with a concretionary or radiated fibrous structure, or even stalactites or encrustations. It also forms finger-staining earthy masses, as well as dendritic aggregates in cracks in rocks, sometimes mistakenly considered "fossil ferns". Opaque, its luster is variable, from matte to sub-metallic and its color is iron black to dark steel gray. Psilomelane can be cut and used in jewelry.

Main photo : Psilomelane from Murzinskoe gold deposit, Krasnoshchyokovsky, Russia © Eugene & Sharon Cisneros

No twins known for this mineral species.

No fakes listed for this mineral species.