psilomelane

from WordNet (r) 3.0 (2006)

psilomelane
    n 1: a mineral consisting of hydrated basic oxide of manganese
         and barium; a source of manganese

from The Collaborative International Dictionary of English v.0.48

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.
   [1913 Webster]