Manganese (IV) oxide

Manganese oxide (IV) (manganese dioxide) MnO2 — powder of dark brown color, insoluble in water. The steadiest compound of manganese, widespread in crust (a mineral manganous peroxide).
At usual conditions behaves quite inertly. When heating with acids shows oxidizing properties, for example, oxidizes concentrated hydrochloric acid to chlorine.
With sulfuric and nitric MnO2 acids decays with release of oxygen.
At interaction with strong oxidizers manganese dioxide is oxidized before the Mn7 connections + and Mn6 + .