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 Huebner 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 (King, 2005).

Composition

Since the 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 the 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 (Errandonea & Segura, 2010). 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 (Neiva, 2008). 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 (King, 2005). 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 (Neiva, 2008). 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 hübenerite has a variation from yellowish-brown to reddish-brown (Errandonea & Segura, 2010). Crystal and crystalline masses of hübenerite show a verity of lusters from adamantine, submetallic to resinous luster (Dutrow & klein, 2007). In thin splints hübenerite can be either transparent or translucent. The streak is related to the color being a shade lighter (King, 2005). All the wolframite family members possess a perfect cleavage on {010}. On {100} and {102} there is less-well developed parting. In hübenerite 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 hübenerite is between 4 and 4.5 and specific gravity between 7.12 and 7.18.

Geological occurrence

Hübenerite is a rare member of the wolframite group. Hübenerite usually found within pegmatites and high-temperature quartz veins. Hübenerite does not occur by itself (Neiva, 2008), but is typically associated with other minerals such as cassiterite, scheelite, quartz, galena, arsenopyrite, native bismuth, pyrite, and sphalerite.

History and uses

Hübenerite was not the original name giving to the mineral. Hübenerite is the synonym of the original name megabasite. The name megabasite was given to mineral by A. Breithaupt in 1852. The name hübenerite was given the mineral by E.N Riotte in 1865 to honor the metallurgist Hüttenmeister Adolph Hübner (King, 2005).

Hübenerite is primarily used as a source of tungsten. Tungsten is used to harden metal in the manufacture of high-speed tools (Dutrow & Klein, 2007).

See also

• List of minerals
• List of minerals named after people

References

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