Doloresite
Chemical formula: V<sup>4+</sup><sub>3</sub>O<sub>4</sub>(OH)<sub>4</sub>
Doloresite is a rare vanadium hydroxide, forming dark, platy crystals and aggregates, valued by collectors of rare minerals.
Properties
- Mohs hardness
- 3.5
- Luster
- Submetallic to metallic
- Streak
- Blackish brown
- Density
- 3.27-3.4
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Doloresite can be identified by its dark, almost black color, metallic luster, and characteristic platy or bladed crystals forming radial aggregates. A key feature is its occurrence in the oxidation zones of uranium-vanadium deposits, often in association with other vanadium minerals. ## Distinguishing from Similar Minerals It can be confused with other vanadium oxides and hydroxides, such as montroseite, paramontroseite, or duttonite. It differs from montroseite in its optical and X-ray properties. Duttonite has a similar composition but crystallizes in a different system (monoclinic) and often has a lighter, greenish-brown color. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Doloresite crystals are most often platy or bladed, elongated in one direction. They usually occur as radial or fibrous aggregates, and also as disseminated flakes in the host rock (mainly in sandstones).
Geological environment
## Genesis Doloresite is a secondary mineral, formed in the oxidation zones of uranium-vanadium deposits. It forms at low temperatures as a result of the alteration of primary vanadium minerals, such as montroseite, under conditions of low redox potential. Its formation is associated with the circulation of groundwater in sedimentary rocks, mainly sandstones. ## Mineral Associations This mineral co-occurs with other vanadium and uranium minerals. It is most commonly associated with: montroseite, duttonite, paramontroseite, corvusite, pascoite, as well as uraninite, carnotite, and tyuyamunite. In the gangue, it associates with quartz, calcite, and clay minerals. ## Localities The most important and well-documented occurrences of doloresite are in the USA, on the Colorado Plateau, particularly in Montrose and Mesa counties (Colorado) and Apache County (Arizona). It is known from many mines in the Uravan district. Outside the USA, its occurrence has been reported in the Shinkolobwe uranium mine in the Democratic Republic of Congo.
Rarity
Rare
For collectors
## Quality Criteria The most prized by collectors are specimens with well-formed, sharp crystals forming aesthetic, radial aggregates. Contrast with the light host rock (sandstone) is also important. Large, rich doloresite aggregates are rare and command higher value. Specimen purity and lack of mechanical damage are crucial. ## Popular Localities Classic and most sought-after specimens come from historical localities in Colorado, USA, such as the La Dolores mine (type locality), Jo Dandy mine, or Vanadium Queen mine. Specimens from these locations are considered exemplary for this mineral species.
Care and storage
## Cleaning Doloresite specimens should be cleaned very carefully, preferably using compressed air to remove dust. Due to its potential sensitivity to water and chemicals, wet cleaning should be avoided. If absolutely necessary, a soft, dry brush can be used. ## What to Avoid Avoid contact with water, acids, and other chemical agents that may cause its decomposition or discoloration. The mineral is relatively soft and brittle, so it must be protected from impacts and scratches. It should not be heated or exposed to prolonged humidity. ## Storage It is recommended to store doloresite specimens in dry conditions, preferably in closed collector's boxes or display cases, which protect them from dust, moisture, and mechanical damage. It should be kept away from harder minerals to avoid scratching.