Pyr`o*lu"site (?), n. [Pyro- + Gr. &?; to loose, or &?; a loosing.] (Min.) Manganese dioxide, a mineral of an iron-black or dark steel-gray color and metallic luster, usually soft. Pyrolusite parts with its oxygen at a red heat, and is extensively used in discharging the brown and green tints of glass (whence its name).