Definition
Tungstite is a hydrous tungsten oxide mineral with the chemical formula WO₃·H₂O. It is classified as a secondary oxide mineral that forms through the alteration of primary tungsten‑bearing minerals.
Overview
Tungstite crystallizes in the orthorhombic system, typically occurring as translucent yellow to yellow‑green masses or earthy, pulverulent aggregates. The mineral displays perfect cleavage parallel to the [001] direction and imperfect cleavage along [110]. Its Mohs hardness is approximately 2.5, and it has a specific gravity of about 5.5. Tungstite is most commonly encountered in the oxidized zones of tungsten ore deposits, where it develops as a weathering product of minerals such as wolframite, ferberite, and scheelite. The type locality is the Hubbard Tungsten Mine near Trumbull, Connecticut, United States, where the mineral was first described in 1868.
Etymology / Origin
The name “tungstite” derives from the element tungsten, itself named from the Swedish words tung (“heavy”) and sten (“stone”). The suffix “‑ite” is a standard mineralogical ending indicating a naturally occurring solid.
Characteristics
| Property | Description |
|---|---|
| Chemical formula | WO₃·H₂O |
| IMA symbol | Tgs |
| Strunz classification | 4.FJ.10 (hydroxide minerals) |
| Crystal system | Orthorhombic (space group Pmnb) |
| Color | Yellow, yellow‑green, or orange‑yellow |
| Crystal habit | Earthy, pulverulent masses; sometimes granular or fibrous |
| Cleavage | Perfect on {001}, imperfect on {110} |
| Mohs hardness | 2.5 |
| Luster | Resinous to pearly |
| Streak | Yellow |
| Diaphaneity | Transparent to translucent |
| Specific gravity | ~5.5 |
| Optical properties | Biaxial (‑); refractive indices nα = 2.090, nβ = 2.240, nγ = 2.260; birefringence δ = 0.170 |
| Formation | Secondary mineral produced by oxidation and hydration of primary tungsten ores (e.g., wolframite, ferberite) in near‑surface environments. |
| Occurrences | Reported from oxidized tungsten deposits in the United States, Canada, Brazil, China, Portugal, and several African localities. |
Related Topics
- Tungsten minerals – a group that includes wolframite, scheelite, ferberite, and other primary tungsten ores.
- Wolframite – a major tungsten ore that commonly weathers to form tungstite.
- Scheelite – calcium tungstate (CaWO₄), another primary source of tungsten that can alter to tungstite under oxidizing conditions.
- Ferberite – the iron‑rich endmember of the wolframite series, also a precursor to tungstite.
- Hydrous oxide minerals – a class of minerals containing water molecules within their crystal structures, of which tungstite is a member.
- Mineral classification systems – such as the Strunz and Dana systems, which place tungstite in the hydroxide/oxide categories.
Sources: Wikipedia entry on Tungstite, Mindat.org mineral database, standard mineralogical literature.