Mesaite
Chemical formula: CaMn<sup>2+</sup><sub>5</sub>(V<sup>5+</sup><sub>2</sub>O<sub>7</sub>)<sub>3</sub>·12H<sub>2</sub>O
Mesaite is a very rare, hydrated calcium and manganese vanadate, forming microscopic, yellowish-orange crystals in uranium-vanadium deposits.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous, Pearly
- Streak
- Pale yellow
- Density
- 2.61
- Cleavage
- Perfect on {010}
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The characteristic features of mesaite are its orange-yellow color, the specific form of small, bladed crystals forming rosettes, and its occurrence in paragenesis with other secondary vanadium minerals. Due to the microscopic size of the crystals, definitive identification is possible almost exclusively by advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Mesaite can be confused with other brightly colored vanadates. It is distinguished from pascoite by its lighter, more yellow hue (pascoite is typically reddish-orange). Carnotite and tyuyamunite usually have a brighter yellow color and often form powdery or earthy coatings, in contrast to the distinct, though small, crystals of mesaite. ## Crystal Forms Crystals are very small, thin, tabular or bladed. They often arrange themselves into radial groups, fans, and rosettes, forming visually attractive microscopic aggregates.
Geological environment
## Genesis Mesaite is a secondary mineral, forming in the oxidation zones of uranium-vanadium deposits in sandstones. It crystallizes from vanadium-rich waters that permeate sedimentary rocks, under conditions of low temperature and pressure. ## Mineral Associations This mineral co-occurs with other secondary vanadates, such as pascoite, sherwoodite, as well as montroseite, carnotite, tyuyamunite, and gypsum. ## Localities The most important and classic localities for mesaite are in the USA, in the Uravan mineral belt, on the border of Colorado and Utah. The type locality is the Jo Dandy mine in Montrose County, Colorado. Other known occurrences include mines in the La Sal area of San Juan County, Utah.
Rarity
Very rare
For collectors
## Quality Criteria The collector's value of mesaite specimens depends on several factors. The most prized samples are those with rich, dense clusters of well-formed, though microscopic, crystals. The intensity and purity of the orange-yellow color also enhance its attractiveness. The contrast with the host rock color and aesthetic associations with other minerals are also important. ## Popular Localities Almost all specimens available on the collector's market come from classic localities in the Uravan belt in the USA (Colorado and Utah). Specimens from the Jo Dandy mine, as the type locality, are particularly sought after by specialized collectors.
Care and storage
## Cleaning Mesaite specimens are extremely delicate and should be handled with the utmost care. For dust removal, it is best to use a soft, dry brush or a photographic air blower. Contact with water should be strictly avoided, as, being a hydrated mineral, it may dissolve or alter. ## What to Avoid Avoid all chemicals, ultrasonic cleaners, and high temperatures, which can cause dehydration and destruction of the mineral's structure. It is very soft, so it must be protected from scratches and impacts. ## Storage It is recommended to store specimens in closed, padded "perky boxes" to protect them from mechanical damage, dust, and humidity changes. Avoid exposure to direct sunlight.