Psilomelane – general formula: (Ba,H₂O)₂Mn₅O₁₀ – does not designate a mineral species. It is an old term, nowadays less used, referring to a set of black, hard and hydrated oxides of manganese that can contain Ba, Cu, Co, Ni, Mg, Ag, Ca, W and K. It is a mining term, very practical, used when it is impossible or when the exact mineralogical determination of Mn ores is not necessary. Generally psilomelane is formed by mixtures of several manganese minerals – oxides and hydroxides – very similar to each other.

Among the minerals that make up psilomelane, romanechite is mainly found. Besides it, polyanite (well-crystallized pyrolusite), bixbyite, braunite, hausmannite, cryptomelane, hollandite, coronadite, rancieite, goethite and quartz. In common, their mamelon/botryoidal structure of extremely small crystals, at the limit of microscopic observation. Chemically, its composition naturally varies a lot, it contains between 70 and 80% Mn oxide. Another mining term used in connection with these hydrated black manganese mixtures is “wad”.

Psilomelane is a common and important ore of manganese, occurring under the same conditions and having the same commercial applications as pyrolusite. Psilomelane is often banded with gray pyrolusite and these alternating gray and black layers form very diverse structures. Psilomelane can also form tufts of hair crystals similar to those formed by pyrolusite. Generally, the difference in the brightness of the two minerals allows them to be distinguished: pyrolusite is gray with a metallic luster and psilomelane is black with a submetallic luster. When earthy and dull, they are difficult to differentiate, but pyrolusite is soft (stains the paper at scratch) while psilomelane is much harder. Psilomelane slowly effervesces with H₂O₂.