Tungstite
Chemical formula: W<sup>6+</sup>O<sub>3</sub>·H<sub>2</sub>O
Tungstite is a hydrated tungsten oxide, forming characteristic yellow, earthy coatings and encrustations on tungsten minerals.
Properties
- Mohs hardness
- 2.5
- Luster
- Earthy
- Streak
- Yellow
- Density
- 5.5
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification The key diagnostic feature of tungstite is its characteristic, bright yellow or yellowish-green color and its occurrence as earthy, powdery coatings directly on tungsten minerals, such as wolframite or scheelite. It is very soft and easily scrapes off with a fingernail. ## Distinguishing from Similar Minerals It can be confused with other secondary uranium minerals (e.g., carnotite) or molybdenum minerals (e.g., molybdenite), which also form yellow coatings. However, tungstite is distinguished by its geological context – a close association with tungsten minerals. Unlike uranium minerals, tungstite is not radioactive. ## Crystal Forms Most often, it forms microcrystalline, earthy, and powdery aggregates. Distinct crystals are rarely observed, taking the form of small, hexagonal plates or lamellae, often gathered in rosetted clusters.
Geological environment
## Genesis Tungstite is a secondary mineral, formed exclusively in the oxidation (weathering) zones of tungsten ore deposits. It forms as a result of the chemical decomposition of primary tungsten minerals, mainly wolframite ((Fe,Mn)WO₄) and scheelite (CaWO₄), under the influence of oxygen-rich surface waters. ## Mineral Associations It always occurs in association with the minerals from which it formed, namely wolframite and scheelite. It often co-occurs with quartz, as well as with other oxidation products, such as hematite, goethite, ferberite, and sometimes copper or bismuth minerals. ## Localities Significant tungstite localities are found in many places around the world where tungsten deposits are exploited. Classic localities include the Caldbeck Fells mine in Cumbria (England), mines around Trumbull in Connecticut (USA), the Panasqueira deposit (Portugal), as well as numerous sites in Bolivia, Peru, China, and Australia.
Rarity
Not very common
For collectors
## Quality Criteria The most prized specimens by collectors are those where tungstite forms well-developed, even microscopic, crystals in the form of lamellae or rosettes. Samples with intensely colored, thick coatings on a contrasting substrate, such as dark wolframite or white quartz, are also highly valued. The aesthetic composition and lack of damage to the delicate mineral layer are important. ## Popular Localities The historical locality in Trumbull, Connecticut (USA), which has yielded specimens with relatively large crystals, is considered classic and provides some of the best specimens. High-quality microcrystals also come from the Clara mine in the Black Forest (Germany) and from some localities in China, such as the Xihuashan mine in Jiangxi Province.
Care and storage
## Cleaning Tungstite specimens are extremely delicate, especially those in the form of earthy coatings. Wet cleaning should be avoided. The safest method is to gently remove dust with a soft brush or a photographic air blower. Ultrasonic cleaners should not be used. ## What to Avoid Contact with water and chemicals, which can dissolve or damage delicate coatings, must be absolutely avoided. The mineral is soft and brittle, susceptible to scratching and abrasion. It should be protected from vibrations and impacts. ## Storage It is recommended to store specimens in closed, padded collector boxes to protect them from dust, mechanical damage, and moisture. Display should be in stable conditions, away from sources of vibration.