pyrolusite

This term refers specifically to the most common mineral form of manganese dioxide. It is characterized by its dark, often black or grayish appearance and is primarily recognized in geological and industrial contexts for its role as a catalyst and a source of manganese.

As a mass noun representing a chemical substance and mineral species, it is treated as uncountable. To refer to specific quantities or distinct samples, speakers must use partitive constructions such as a sample of pyrolusite or a deposit of pyrolusite.