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.
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.
External links
Wikimedia Commons has media related to Braunite.References
JoHan P. R. De Viliers, The crystal structure of braunite II and its relation to bixbyite and braunite, American Mineralogist, Volume 65, pages 756–765, 1980 http://www.minsocam.org/ammin/AM65/AM65_756.pdf ↩
Mindat, Braunite-II http://www.mindat.org/min-4860.html ↩