Pyrolusite

Identifying the manganese oxide minerals is a crapshoot without expensive lab equipment, so generally black dendrites and crystalline occurrences are called pyrolusite while black crusts are called psilomelane. There is an acid test for manganese oxides, which is that they dissolve in hydrochloric acid with the release of nasty-smelling chlorine gas. Manganese oxides are secondary minerals that form by weathering of primary manganese minerals like rhodochrosite and rhodonite or by deposition from water in bogs or the deep sea floor as manganese nodules.

Other Diagenetic Minerals