braunite

{{Infobox mineral | name = Braunite | image = Braunit - San Marcel, Piemont.jpg | imagesize = 260px | alt = | caption = Braunite, from San Marcel, Piemonte, Italy | category = Nesosilicates | formula = Mn2+Mn3+6[O8|SiO4] | IMAsymbol=Bnt | molweight = | strunz = 9.AG.05 | dana = 7.5.1.3 | system = Tetragonal | class = Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) | symmetry = I41/acd | unit cell = | color = brownish black, steel-grey | colour = | habit = | twinning = | cleavage = {112} perfect | fracture = | tenacity = | mohs = 6– | luster = sub-metallic | streak = black | diaphaneity = opaque | gravity = 4.72 – 4.83 | density = | polish = | opticalprop = | refractive = | birefringence = | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | prop1 = | prop1text = | references = | var1 = | var1text = }}

Braunite is a silicate mineral containing both di- and tri-valent manganese with the chemical formula: Mn2+Mn3+6[O8|SiO4]. Common impurities include iron, calcium, boron, barium, titanium, aluminium, and magnesium.