Braunite

Braunite is a silicate mineral containing both di- and tri-valent manganese with the chemical formula: Mn²⁺Mn³⁺₆[O₈|SiO₄].^[3] Common impurities include iron, calcium, boron, barium, titanium, aluminium, and magnesium.

Braunite
Braunite, from San Marcel, Piemonte, Italy
General
Category	Nesosilicates
Formula	Mn2+Mn3+6[O8|SiO4]
IMA symbol	Bnt[1]
Strunz classification	9.AG.05
Dana classification	7.5.1.3
Crystal system	Tetragonal
Crystal class	Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m)
Space group	I41/acd
Identification
Color	brownish black, steel-grey
Cleavage	{112} perfect
Mohs scale hardness	6–6+1⁄2
Luster	sub-metallic
Streak	black
Diaphaneity	opaque
Specific gravity	4.72 – 4.83
References	[2]

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.^[3]

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]