CHEMISTRY MnO2 Manganese oxide
CRYSTALLOGRAPHY Tetragonal
CRYSTAL GROWTH AND HABITS Pyrolusite forms prismatic crystals that have a square cross section and are usually fibrous. It is usually fine (powdery) granular to massive but can also be reniform, dendritic and concretionary.
COLOR AND OTHER OPTICAL PROPERTIES Pyrolusite is gray to black, sometimes with a bluish cast. It is opaque.
HARDNESS 6 - 6.5
SPECIFIC GRAVITY 5.0 - 5.2 for crystals and less for massive varieties
LUSTER Pyrolusite has a metallic to dull appearance for crystals and earthy for the massive varieties
STREAK Black
BREAKABILITY Crystals have good cleavage in one direction, but the massive form has uneven fracture.
OCCURRENCE Pyrolusite is found in the oxidized zone of manganese deposits.
ASSOCIATED MINERALS Manganite, goethite, hematite
NAME From the Greek "pyro" for fire and "louein" to wash. It was used to remove "wash-out" the greenish color in glass caused by iron.