Braunite – Occurrence, Properties, and Distribution

Braunite was named after Wilhelm von Braun, an Advisor of the Chambers, in Gotha, Germany. He was also a supporter of geology and mineralogy, and provided the original material for the description of braunite.

Properties of Braunite

The following are the key properties of braunite:

  • Cell Data
    • Space group: I41/acd
    • a = 9.36-9.45
    • c = 18.60-18.97
    • Z = 2
  • Crystal Data
    • Tetragonal
    • Point group: 4/m2/m2/m
    • As pyramidal crystals, to 5 cm, striated on {001} and {201} || [010]
    • Dense granular, massive
    • Twinning: On {112}
    • X-ray powder pattern: 2.72 (100), 1.656 (70), 2.14 (50), 2.35 (40), 1.420 (40), 1.074 (40), 3.49 (30)
  • Chemical Composition
    Elements Content 1 Content 2 Content 3
    MnO 78.91 [10.80] 11.73
    Mn2O3 [75.80] 78.33 -
    SiO2 9.89 9.68 9.94
    O 7.35 - -
    FeO 3.81 - -
    Fe2O3 - 2.02 -
    CaO 0.34 0.38 -
    Al2O3 - 0.35 -
    MgO 0.15 0.13 -
    TiO2 - 0.09 -
    Total 100.45 [99.25] 100.00
  • Optical Properties
    • R1-R2: (400) 23.4-25.4, (420) 22.7-24.5, (440) 22.0-23.6, (460) 21.5-22.9, (480) 21.0-22.4, (500) 20.5-21.9, (520) 20.0-21.5, (540) 19.6-21.2, (560) 19.3-20.9, (580) 19.0-20.6, (600) 18.8-20.3, (620) 18.6-20.0, (640) 18.5-19.8, (660) 18.3-19.6, (680) 18.2-19.5, (700) 18.1-19.4
    • Anisotropism: Weak in air to distinct in oil, dark to lighter slate gray
  • Estimated Properties
    Electron density Bulk density (electron density) = 4.61 g/cm3
    note: Specific gravity of braunite = 4.89 g/cm3
    Photoelectric PEBraunite = 16.86 barns/electron
    U=PEBraunite x ρ electron density= 77.73 barns/cm3
    Fermion index Fermion index = 0.0023216105
    Boson index = 0.9976783895
    Radioactivity Braunite is not radioactive

How to Identify Braunite

Braunite can be identified in the field by its color variations between grayish black, brownish gray, and dark brownish black. Its opaque form has {111} perfect cleavage. This mineral has a sub-metallic luster with brownish gray black streak. The fracture on this mineral is brittle. The density of braunite is 4.72 - 4.82 g/cm3 with a hardness of 6-6.5 - between that of orthoclase and pyrite.

Global Distribution

Braunite is distributed in the following places:

  • Germany - At Ohrenstock and Elgersburg, near Ilmenau, Thuringia, and at Ilfeld, Harz Mountains
  • Norway, at Botnedalen
  • Sweden - From Langban, and Jakobsberg, Varmland,
  • India - From Kacharwali, Nagpur district, Maharashtra, and Tirodi, Madhya
  • Pradesh
  • Brazil - At Miguel Burnier, near Ouro Preto, Minas Gerais
  • South Africa - From mines in the Kalahari manganese field, around Kuruman, Cape Province
  • Italy – At St. Marcel, Val d'Aosta
  • USA - At the Spiller manganese mines, 25 km northeast of Mason, Mason Co., Texas; in the Batesville district, Independence Co., Arkansas; at Cartersville, Bartow Co. Georgia; from Snowmass, Pitkin Co., Colorado; in the Black Diablo mine, Pershing Co., Nevada; and the Fort Seward mine, Humboldt Co., California.

Occurrence of Braunite and Useful Mineral Association

Braunite occurs by metamorphism of manganese silicates and oxides; and also as a product of weathering. It is often associated with minerals such as pyrolusite, hausmannite, bixbyite, rhodonite, jacobsite, spessartine, and hematite.

References

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