| Braunite | |
| Category: | Nesosilicates |
| Formula: | Mn2+Mn3+6[O<sub>8</sub>|SiO<sub>4</sub>]| IMAsymbol=Bnt[1] | 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 = 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 = [2] | var1 = | var1text = }} Braunite is a silicate mineral containing both di- and tri-valent manganese with the chemical formula:Mn2+Mn3+6[O<sub>8</sub>|SiO<sub>4</sub>].[3] Common impurities include iron, calcium, boron, barium, titanium, aluminium, and magnesium. Braunite forms grey/black tetragonal crystals and has a Mohs hardness of 6 – 6.5. It was named after the Wilhelm von Braun (1790–1872) of Gotha, Thuringia, Germany. A calcium iron bearing variant, named braunite II (formula: Ca(Mn3+,Fe3+)14SiO24), was discovered and described in 1967 from Kalahari, Cape Province, South Africa.[4] [5] External links} |