Pascoite

Chemical formula: Ca<sub>3</sub>[V<sup>5+</sup><sub>10</sub>O<sub>28</sub>]·17H<sub>2</sub>O

Pascoite is a rare, bright orange vanadium mineral, forming characteristic encrusting aggregates on host rocks.

## Characteristics Pascoite is a hydrated calcium vanadate, known for its intense, orange-red to yellowish-orange color. It typically occurs as thin encrustations, coatings, and earthy or powdery aggregates. Less commonly, it forms small, elongated crystals with a platy or acicular habit, which can form radiating aggregates. Due to its vivid color, it is easily noticeable against the rocks on which it forms. ## Physical Properties This mineral is very soft, with a Mohs hardness of approximately 2.5, meaning it can be scratched with a fingernail. It has a dull, earthy luster, and in the case of better-formed crystals, a vitreous to pearly luster. It is a light mineral, with a density of about 2.46 g/cm³. Crystals can be transparent to translucent, while encrusting aggregates are usually opaque. ## Colors and Varieties The dominant and essentially only color of pascoite is bright orange-red, which can transition to yellowish-orange hues. No color or commercial varieties are distinguished. ## History and Name The mineral's name comes from the Pasco Province in Peru, where it was first found and described. The discovery was made in the Minas Ragra mine. The mineral was scientifically described by William F. Hillebrand and co-workers in 1914. ## Uses Pascoite, due to its rarity, softness, and small crystal size, has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or vanadium minerals.

Properties

Mohs hardness
2.5
Luster
Vitreous to Pearly
Streak
Pale orange-yellow
Density
2.46
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The most important diagnostic feature of pascoite is its intense, orange-red color and its occurrence as encrustations and coatings. Its low hardness and reaction to water (solubility) are also characteristic. The streak is a lighter, yellowish-orange color. ## Distinguishing from Similar Minerals Minerals with similar color and mode of occurrence include other secondary vanadates, such as hewettite and metahewettite. Hewettite usually has a more reddish-brown hue and slightly different physical properties. Final differentiation of these minerals often requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal Forms Pascoite most often forms microcrystalline encrustations and earthy coatings. Well-formed, small crystals with a platy or acicular habit, which can group into radiating or chaotic aggregates, are rarely found.

Geological environment

## Genesis Pascoite is a secondary mineral, forming in the oxidation zones of vanadium ore deposits. It forms in dry, desert climates as a result of weathering and alteration of primary vanadium minerals, such as patronite. It forms as a dehydration product of other hydrated vanadates. ## Mineral Associations This mineral often co-occurs with other secondary vanadium minerals, such as hewettite, metahewettite, rossite, as well as gypsum and other sulfates. At the type locality (Minas Ragra), it was associated with vanadium sulfides. ## Localities The most important and classic locality for this mineral is the Minas Ragra mine in Pasco Province, Peru. It is also known from numerous occurrences in the USA, mainly in the states of Utah, Arizona, Colorado, and New Mexico, where it occurs in sandstone rocks containing uranium and vanadium (Morrison Formation).

Rarity

Rare

For collectors

## Quality Criteria The most valued by collectors are specimens with well-formed, even if small, crystals of intense, bright orange color. Rich coverage of the host rock and contrast with a light background enhance attractiveness. Specimens from the classic locality in Peru (Minas Ragra) are historically valuable, but currently, samples from the USA dominate the market. ## Popular Localities On the collector's market, specimens most often come from uranium-vanadium mines on the Colorado Plateau in the USA, especially from Utah (e.g., San Juan district). Specimens from the type locality in Peru are a rarity.

Care and storage

## Cleaning Pascoite specimens are extremely delicate and sensitive to water. Mechanical cleaning is highly inadvisable. Any dust should be removed very carefully using a soft brush or a photographic air blower. Contact with water, which can dissolve or damage the mineral, should be avoided. ## What to Avoid Pascoite is a mineral soluble in water and acids. Contact with any liquids, including distilled water, must be strictly avoided. The mineral is also very soft and brittle, susceptible to scratches and mechanical damage. It should be protected from high temperatures and direct sunlight, which can cause dehydration and changes in its properties. ## Storage Specimens should be stored in a dry place, preferably in a closed, airtight container (e.g., a "membrane box" type or a box with a desiccant), to protect them from atmospheric moisture. Due to its brittleness, it should be stored separately, away from harder minerals.

External references

Sources

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