Wolframite
Wolframite is chemically intermediate between Hübnerite and Ferberite with unspecified chemical composition. Wolframite is actually a series between these two minerals. Hübnerite is the Manganese rich end member and 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. Only specimens that are more than 80% pure manganese are called Hübnerite and only specimens more than 80% pure iron are called Ferberite.
There are many localities worldwide for Worlframite. Possibly the largest and best specimens are from the Guangdong and Hunan Provinces, China.
| Chemical Formula: | (Fe2+;Mn2+)WO4 |
| Iron Manganese Tungstate | |
| Molecular Weight: | 303.24 gm |
| Composition: | Manganese | 9.06 % | Mn | 11.70 % | MnO |
| Iron | 9.21 % | Fe | 11.85 % | FeO | |
| Tungsten | 60.63 % | W | 76.46 % | WO3 | |
| Oxygen | 21.10 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | As wedge-shaped crystals, typically flattened {100} and elongated along [010] or, less commonly, along [001], to 15 cm; faces striated k [001] or [010]; in groups of bladed crystals; massive. |
| Twinning: | Contact twins with composition plane {100} or {023}, or more rarely {001}; also interpenetrant or lamellar. |
| Cleavage: | Perfect on {010}, Parting on {100} and {102} |
| Fracture: | Irregular/Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 4.0 – 4.5 |
| Density: | 7.58 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Other: | Slightly magnetic. Decomposed by aqua regia with the separation of tungstic oxide. Forms pseudomorphs after Scheelite. Often more or less completely replaced by Scheelite. Pseudomorphs of Quartz, Hematite, Marcasite, and Kaolinite after Wolframite noted. |
| Color: | Black; dark Brown in transmitted light |
| Transparency: | Opaque |
| Luster: | Submetallic to Metallic Adamantine |
| Refractive Index: | R1–R2: (400) 16.5–19.5, (420) 16.4–19.2, (440) 16.3–18.9, (460) 16.2–18.7, (480) 15.9–18.5, (500) 16.0–18.7, (520) 16.0–18.7, (540) 16.0–18.7, (560) 16.0–18.7, (580) 15.8–18.6, (600) 15.8–18.6, (620) 15.7–18.6, (640) 15.6–18.5, (660) 15.5–18.3, (680) 15.4–18.1, (700) 15.5–18.0 |
| Birefringence: | 0.000 (Opaque) |
| Anisotrophism: | Distinct; Bireflectance: Weak |
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