Pyrolusite and psilomelane. Cut and polished section of a mixture of manganese mineral ores. Pyrolusite (silver grey) is manganese oxide (MnO2) or hydroxide, formed by oxidation of weathered manganese minerals. It is the most common manganese mineral and is an important ore for this metal. The background matrix is another manganese mineral, psilomelane (black). Manganese is a valuable metal since it is an essential ingredient in steel and other alloys. This specimen is 11.5 centimetres wide.
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