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Webster 1913 Edition

Noun.

[Gr. [GREEK] bare + [GREEK], [GREEK], black.]

(Min.)

A hydrous oxide of manganese, occurring in smooth, botryoidal forms, and massive, and having an iron-black or steel-gray color.

psilomelane ‎(usually uncountable, plural psilomelanes)

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