Pyrolusite is one of about two or three dozen blackish-colored manganese oxide or hydroxy-oxide minerals. Distinguishing pyrolusite (MnO2 - manganese dioxide) from other Mn-oxides requires careful chemical analysis. Pyrolusite, and Mn-oxides in general, have a reflective black color. Pyrolusite (see sample below) has a metallic luster, a black streak, a hardness from about 1 to over 6, and often forms radiating acicular crystal clusters.
Pyrolusite is the most important manganese ore mineral. Among other things, the Mn from pyrolusite is used in the steel-making process.
Pyrolusite (4.6 cm across)