Hübnerite

Hübnerite or hubnerite is a mineral consisting of manganese tungsten oxide (chemical formula MnWO₄). 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 n_α = 2.170 – 2.200, n_β = 2.220, and n_γ = 2.300 – 2.320.

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.

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 . The predominance of either iron or manganese results in formation of one of two minerals, the compositional end-members (ferberite) and (hübnerite), respectively. These compounds are usually referred to as "wolframites" because they share the wolframite structure, but are not naturally occurring minerals, typically being produced for industrial applications, e.g., crystal scintillators.

Structure

thumb|upright=0.7|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)

Hübnerite is a rare end-member of the wolframite group, and has the same crystal structure as other members of the family. The crystal structure contains distorted tetrahedral () and octahedral () units. The wolframite family represents complete solid solution between Fe²⁺ and Mn²⁺. Crystal and crystalline masses of hübnerite show a variety of lusters from adamantine, submetallic to resinous luster. In thin splints, hübnerite can be either transparent or translucent. The streak is related to the color being a shade lighter.