psilomelane

Psilomelane is the historical, non-specific name applied to a group of manganese oxide minerals that occur as hard, black to brownish-black, opaque masses. Because the composition and structure vary widely among specimens, psilomelane has not been treated as a single mineral in modern classifications. Specimens labeled as psilomelane typically contain manganese oxide with hydrous components and may incorporate other oxides such as iron, barium, potassium, or copper. In many cases the material is a mixture of cryptomelane, hollandite, and related manganese-oxide minerals rather than a discrete species.

Occurrence and associations: Psilomelane is commonly found in manganese ore deposits and in weathered outcrops; it forms botryoidal, massive, or stalactitic aggregates and is frequently associated with other manganese oxides such as pyrolusite and manganite.

Etymology and nomenclature: The name derives from Greek psilos (bare) and melas (black), referring to its dark, featureless appearance. In modern mineralogy the term psilomelane is regarded as historical; most specimens previously called psilomelane are now classified as cryptomelane, hollandite, or other manganese-oxide minerals; psilomelane continues to appear in older literature and as a historic collecting term.