HUBNERITE

Chemistry: MnWO4, Manganese tungstate
Class: Sulfates
Subclass: Tungstates
Uses: a minor ore of tungsten (an important industrial element) and as a mineral specimen.
Specimens

Hubnerite belongs to a series with another mineral, Ferberite, FeWO4. Hubnerite is the Manganese rich end member while ferberite is the iron rich end member. Wolframite is the name of the series and the name applied to indistinguishable specimens and specimens intermediate between the two end members. Most specimens found in nature fall within 20 - 80% range of the series and these are termed wolframites, (Fe,Mn)WO4. Only if they are more pure than 80% manganese are they called Hubnerite. Hubnerite is more common than ferberite but not nearly as common as wolframite. The iron in wolframite and ferberite cause much of the differences between them and Hubnerite. Hubnerite tends to be light in color, with a lighter streak, more transparent and less dense. Ferberite, however, tends to be black colored, with a black streak, is opaque with a nearly submetallic luster, is denser and weakly magnetic. Wolframite is of course intermediate in characteristics.

Hubnerite can make a valuable and attractive specimen when associated with clear quartz clusters.

PHYSICAL CHARACTERISTICS:

Color is yellow to reddish brown.
Luster is resinous.
Transparency crystals are transparent to translucent.
Crystal System is monoclinic; 2/m
Crystal Habits include the flat, heavily modified, tabular crystals. The crystals are elongated along the c axis and are generally flattened in the a axis direction. Also as columnar aggregates and lamellar masses.
Cleavage is perfect in one direction parallel to the a and c axes.
Fracture is uneven.
Hardness is 4 - 4.5.
Specific Gravity is approximately 7.0 (heavy even for metallic minerals)
Streak is brown or gray.
Associated Minerals are quartz, hematite, tourmalines, cassiterite, micas and pyrite.
Other Characteristics: crystals striated lengthwise.
Notable Occurrences include Nanling Range, China; France; North Carolina, Idaho and Colorado, USA; Russia; Peru; England and Bolivia.
Best Field Indicators are crystal habit, color, density, luster and cleavage.