Macro of a pyrolusite mineral with dendrite crystal formations. It is approximately 3 ½ inches (9 cm) tall. — Photo: “Jonathan Zander (Digon3)" · CC BY-SA 3.0
Pyrolusite
Also known as: Manganese ore.
Manganese dioxide — the classic black dendrite-forming mineral and a major manganese ore.
Intro adapted from Wikipedia (CC BY-SA).
Pyrolusite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula MnO₂.
It crystallizes in the tetragonal crystal system (space group P4_2/mnm). It is a member of the Rutile structural group.
Key properties: Mohs hardness 6–6.5; specific gravity 5.06; typically gray or black; Black, bluish black streak; Metallic luster.
IMA symbol Pyl, IMA status: approved, named in 1827.
Formed under highly oxidizing conditions in manganese-bearing hydrothermal deposits and rocks; in bogs and lakes, under shallow marine conditions; commonly an alteration product of manganite.
It is found associated with Manganite, hollandite, hausmannite, braunite, chalcophanite, goethite, hematite.
Its name comes from the Greek for fire and to wash, as it is used to remove tints from glass.
Collections: Metals & Native Elements, Collector Favorites.