What is "psilomelane"

Psilomelane \Psi*lom"e*lane\, n. [Gr. ? bare + ?, ?, black.] (Min.) A hydrous oxide of manganese, occurring in smooth, botryoidal forms, and massive, and having an iron-black or steel-gray color.

n. Any hard, black hydrous manganese oxide with variable amounts of barium and potassium.

n. a mineral consisting of hydrated basic oxide of manganese and barium; a source of manganese

Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese oxide with variable amounts of barium and potassium. Psilomelane is erroneously, and uncommonly, known as black hematite, despite not being related to true hematite, which is an iron oxide.