Hübnerite

Hubnerite

Hubnerite from Silverton District, San Juan County, Colorado (Size: 8.5 x 6.6 x 4.3 cm)
General
Category Oxide minerals
Formula
(repeating unit)		 MnWO4
Strunz classification 04.DB.30
Crystal symmetry Monoclinic prismatic
H-M symbol: (2/m)
Space group: P 2/c
Unit cell a = 4.86 Å, b = 5.78 Å, c = 5.02 Å; beta = 90.816°, Z = 2
Identification
Color Yellowish brown to reddish brown, blackish brown, black; Deep red internal reflections in reflected light
Crystal habit Prismatic striated crystals, tabular to flattened, in radiating groups
Crystal system Monoclinic
Twinning Contact twins
Cleavage Perfect on {010}
Fracture Irregular/uneven
Tenacity Brittle
Mohs scale hardness 4-4½
Luster Metallic to adamantine towards resinous.
Streak Yellow to reddish brown, greenish gray
Diaphaneity Transparent to translucent
Specific gravity 7.12 - 7.18
Optical properties Biaxial (+)
Refractive index nα=2.17-2.2, nβ=2.22, nγ=2.3-2.32
Birefringence 0.1200-0.1300
Pleochroism Perceptible; X = yellow to green, red-orange; Y = yellowish brown to greenish yellow, red-orange to red; Z = green; brick-red to red
2V angle 73° measured
References [1][2][3]

Hübnerite or hubnerite is a mineral consisting of manganese tungsten oxide (chemical formula: MnWO4, it isn't a tungstate). It is the manganese endmember of the manganese - iron wolframite solid solution series. It forms reddish brown to black monoclinic prismatic submetallic crystals. The crystals are typically flattened and occur with fine striations. It has a high specific gravity of 7.15 and a Mohs hardness of 4.5. It is transparent to translucent with perfect cleavage. Refractive index values are nα=2.170 - 2.200, nβ=2.220, and nγ=2.300 - 2.320.

Sample from the Pasto Bueno District, Pallasca Province, Ancash Department, Peru, showing deep red internal reflections when backlit (Size: 6.6 x 4.2 x 1.6 cm)

Typical occurrence is in association with high-temperature hydrothermal vein deposits and altered granites with greisen, granite pegmatites and in alluvial deposits. It occurs associated with cassiterite, arsenopyrite, molybdenite, tourmaline, topaz, rhodochrosite and fluorite.[1]

It was first described in 1865 for an occurrence in the Erie and Enterprise veins, Mammoth district, Nye County, Nevada, and named after the German mining engineer and metallurgist, Adolf Hübner from Freiberg, Saxony.[1][3]

Introduction

Hübnerite is a rare mineral from the rare family wolframite. It is considered to be one of the principle ores of tungsten. It is usually identified by the dark color, one direction of perfect cleavage and high specific gravity all serving to distinguish it from other minerals. The first recorded identification of the wolframite family was back in 1948 but it was not added as a mineral until 1951.[4]

Composition

Since hübnerite comes from a family with only two end members it would be easier to explain the composition of the wolframite family since there is not enough data on hübnerite itself. The primary formula of the wolframite series is (Fe,Mn)WO4. The domination of either iron or manganese would result in forming one of two minerals. The iron dominated one will result in forming ferberite while the manganese dominated one will result in forming hübnerite.[5] Hübnerite is rarer than ferberite due to the difficulty of iron and manganese substitution. There is also a magnesium substitution involved to form an MgWO4.[6] This magnesium rich usually referred to as wolframite but it is not a mineral it is a crystal scintillator.

Structure

As hübnerite is a rare endmember of the wolframite group the structure of the family will be the structure of the members. Distorted tetrahedral (WO4) and octahedral ((Fe. Mn)O6) is the usual structure of all member in the wolframite family. Complete solid solution occurs between Fe2+ and Mn2+ in the members of the series.[4] In ferberite the percentage of WO3 is around 76.3% while in hübnerite the percentage is around 76.6%. In natural occurrence the percent range fall within 20-80 percent of the wolframite series. In the past it was thought the wolframite family possess orthorhombic symmetry but in fact it is possess monoclinic symmetry. Short prismatic, flattened or wedge-shaped are the common crystals of the wolframite itself. In some rare occasions the crystals occur doubly terminated. It is common for the faces to striated parallel to the c axis.[6] In most cases wolframite is embedded in quartz as subparallel crystalline masses.

Physical properties

The color difference in the members is clear and marked. The color of hübnerite has a variation from yellowish-brown to reddish-brown.[5] Crystal and crystalline masses of hübnerite show a verity of lusters from adamantine, submetallic to resinous luster.[7] In thin splints, hübnerite can be either transparent or translucent. The streak is related to the color being a shade lighter.[4] All the wolframite family members possess a perfect cleavage on {010}. On {100} and {102} there is less-well developed parting. In hübnerite the fracture is brittle and uneven. Is common for all members of the wolframite to show simple contact twins on {100} or rarely interpenetrant twins on {001}. The hardness of hübnerite is between 4 and 4.5 and specific gravity between 7.12 and 7.18.

Geological occurrence

Hübnerite is a rare member of the wolframite group. Hübnerite usually found within pegmatites and high-temperature quartz veins. Hübnerite does not occur by itself,[6] but is typically associated with other minerals such as cassiterite, scheelite, quartz, galena, arsenopyrite, native bismuth, pyrite, and sphalerite.

History and uses

Hübnerite was not the original name giving to the mineral. Hübnerite is the synonym of the original name megabasite. The name megabasite was given to mineral by A. Breithaupt in 1852. The name hübnerite was given the mineral by E.N Riotte in 1865 to honor the metallurgist Adolph Hübner.[4]

Hübnerite is primarily used as a source of tungsten. Tungsten is used to harden metal in the manufacture of high-speed tools.[7]

See also

References

  1. 1 2 3 "Hübnerite Mn2+WO4" (PDF). Mineral Data Publishing. 2005.
  2. ↑ Dave Barthelmy. "Hubnerite Mineral Data". webmineral.com.
  3. 1 2 "Hübnerite". mindat.org.
  4. 1 2 3 4 King, R. J. (2005). "Mineral Explained". Geology Today 21 (1): 33–37. doi:10.1111/j.1365-2451.2005.00493.x.
  5. 1 2 Errandonea, D.; Segura, A. (2010). "High-pressure phase transition and compressibility of wolframite-type tungstates". Journal of Applied Physics 107 (8): 127–142. doi:10.1063/1.3380848.
  6. 1 2 3 Neiva, A. M. R. (2008). "Geochemistry of cassiterite and wolframite from tin and tungsten quartz in Portugal". Ore Geology Reviews (33): 221–238.
  7. 1 2 Dutrow, B.; Klein, C. (2007). "Tungstates and Molybdates". Mineral Science (21): 425–427.
  • Hu, W.B.; Nie, X.L.; Mi, Y.Zh. (2010). "Controlled synthesis and structure characterization of nanostructured MnWO4". Materials Characterization 61 (6): 85–89. doi:10.1016/j.matchar.2009.10.009. 
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