Mendozavilite-KCa

Chemical formula: [K<sub>2</sub>(H<sub>2</sub>O)<sub>15</sub>Ca(H<sub>2</sub>O)<sub>6</sub>][Mo<sup>6+</sup><sub>8</sub>P<sub>2</sub>Fe<sup>3+</sup><sub>3</sub>O<sub>34</sub>(OH)<sub>3</sub>]

Mendozavilite-KCa is a very rare, secondary molybdate with a complex chemical composition, forming microscopic, platy crystals of a yellow-orange color.

## Characteristics Mendozavilite-KCa is a complex phosphate-molybdate of iron, potassium, and calcium. It occurs as very small, thin, platy crystals, often forming rosetted or spherical aggregates. Due to the microscopic size of the crystals, its visual features are difficult to observe without magnification. It is a secondary mineral, forming in the oxidation zones of molybdenum deposits. ## Physical Properties Crystals exhibit a yellow-orange color and a vitreous luster. The mineral is transparent to translucent. Its Mohs hardness is 2.5, and its density is calculated at 3.26 g/cm³. It is a brittle mineral. ## Colors and Varieties This mineral occurs in shades from yellow to orange-yellow. No varieties have been distinguished. ## History and Name The name "Mendozavilite-KCa" refers to its chemical composition, indicating the dominance of potassium (K) and calcium (Ca) in specific structural positions. It is a member of the mendozavilite group, named after Ricardo N. de Mendoza, an Argentine geologist. The mineral was approved by the IMA in 2017 under number 2017-004. ## Applications Due to its extreme rarity and microscopic size, Mendozavilite-KCa has no industrial applications. It is solely of scientific interest and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
2.5
Luster
Vitreous
Streak
Light yellow
Density
3.26
Cleavage
Perfect on {0001}
Fracture
Micaceous
Transparency
Transparent to Translucent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of Mendozavilite-KCa is possible almost exclusively using advanced analytical methods, such as Raman spectroscopy, X-ray diffraction (XRD), and chemical analysis (EDS/WDS). Visual recognition is impossible in field conditions and in a collection. Its characteristic yellow-orange color, platy crystal habit, and occurrence in the oxidation zones of molybdenum deposits are distinctive. ## Distinguishing from Similar Minerals It can be confused with other secondary molybdates, such as wulfenite, powellite, or other members of the mendozavilite group. Differentiation requires specialized laboratory tests to confirm its unique chemical composition and crystal structure. ## Crystal Forms It forms very thin, platy crystals with a hexagonal outline, usually less than 0.1 mm in size. These crystals often group into rosetted or spherical aggregates.

Geological environment

## Genesis It is a secondary mineral, formed as a result of weathering (oxidation) processes of primary molybdenum sulfides (mainly molybdenite) in the presence of minerals containing phosphorus, iron, potassium, and calcium. It forms under low temperature and pressure conditions, in a dry or semi-arid climate. ## Mineral Associations It most commonly co-occurs with molybdenite, pyrite, quartz, as well as other secondary molybdates and sulfates. At its type locality (Cumobabi mine), it was found in association with powellite and quartz. ## Localities The only confirmed and described locality for this mineral is the Cumobabi mine in the municipality of Cumpas, Sonora state, Mexico. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of Mendozavilite-KCa specimens is assessed primarily based on the richness and aesthetics of crystal aggregates on the rock matrix. Due to the microscopic size of the crystals, specimens are evaluated under magnification. The most desirable specimens are those with well-formed, clearly visible rosettes or spherical clusters of intense, yellow-orange color, contrasting with the substrate. ## Popular Localities The only source of Mendozavilite-KCa specimens is the Cumobabi mine in Mexico. All materials available on the collector's market originate from this single locality.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to its brittleness and chemical reactivity, contact with water, cleaning solutions, and ultrasonics should be avoided. ## What to Avoid All chemicals, acids, and bases should be avoided. The mineral is likely sensitive to moisture and temperature changes. It should be protected from direct sunlight, which can cause fading. ## Storage It is recommended to store in stable conditions, in a sealed, dry container (e.g., "micromount" type) to protect against dust, moisture, and mechanical damage.

Sources

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