Sep 26 2013
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