Pyrolusite
Image: “Jon Zander (<a href="//commons.wikimedia.org/wiki/User:Digon3" title="User:Digon3">Digon3</a>)" (CC BY-SA 3.0)
Mineral NamePyrolusite
Chemical FormulaMnO2
Mohs Hardness2
Crystal Systemtetragonal
Streak Colorblack to bluish-black
Cleavageperfect on {110}, rarely observed
Fractureuneven to subconchoidal
Specific Gravity4.4
Colorsblack, dark steel-gray, bluish-black
Transparencyopaque
Type LocalityWorldwide, common in manganese deposits
Mineral GroupOxides
Usesmanganese ore, steel production, dry cell batteries, glass decolorizer, pigment, collector's item
Associated Mineralsmanganite, psilomelane, hematite, goethite, limonite, quartz, calcite
Rarityuncommon
Description
A piece of host rock, likely a sedimentary rock, displaying intricate black, fern-like pyrolusite dendrite patterns across its greenish-yellow and brown surface.
Geological Context
Pyrolusite dendrites form when manganese-rich solutions penetrate tiny cracks and fissures in rocks, precipitating the manganese oxide in a branching, tree-like pattern as the solution evaporates or reacts with the host rock, typically in sedimentary environments.
