Pandoraite-Ca

Chemical formula: CaV₄+₅V₅+₂O₁₆·₃H₂O

Pandoraite-Ca is a very rare vanadate mineral, forming microscopic, black crystals with a metallic luster.

## Characteristics Pandoraite-Ca is a hydrated vanadium and calcium oxide, occurring as very small, bladed or tabular crystals, which rarely exceed 0.2 mm in length. These crystals form rosette-like or randomly oriented aggregates, and sometimes fan-shaped clusters. The mineral is black and opaque. ## Physical Properties Pandoraite-Ca crystals exhibit a strong, metallic luster. Due to the microscopic size of the crystals, hardness has not been precisely measured, but it is estimated to be around 2.5 on the Mohs scale. The density calculated based on the chemical formula and unit cell parameters is 3.25 g/cm³. ## Colors and Varieties The mineral is uniform in color – it occurs exclusively in black. No varieties have been distinguished. ## History and Name Pandoraite-Ca was described as a new mineral in 2023 by Anthony R. Kampf and his team. The name refers to its close chemical relationship with pandoraite, with the addition of the "-Ca" suffix indicating the dominance of calcium in its structure. The name "Pandoraite" comes from the Pandora mine in San Juan County, Utah (USA), where both minerals were discovered. The discovery was approved by the International Mineralogical Association (IMA2022-0 Pandoraite, IMA2022-038 Pandoraite-Ca). ## Uses Due to its extreme rarity and microscopic size, Pandoraite-Ca has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals.

Properties

Mohs hardness: 2.5
Luster: Metallic
Streak: Black
Density: 3.25
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of Pandoraite-Ca is only possible using advanced analytical methods, such as Raman spectroscopy or chemical analysis using an electron microprobe (EDS/WDS). Visually, in the field or in a collection, it can be suspected based on its characteristic form (small, black, bladed crystals with a metallic luster) and co-occurrence with other rare vanadates on sandstone from the type locality (Pandora mine). ## Distinguishing from Similar Minerals Pandoraite-Ca is visually almost identical to pandoraite. Distinguishing these two minerals requires chemical analysis to determine the dominant cation (Ca in Pandoraite-Ca, Ba in pandoraite). It can also be confused with other black, fine-grained vanadium oxides, such as doloresite or montroseite, from which it is distinguished by crystal morphology and chemical composition. ## Crystal Forms The mineral forms very small, thin, bladed or tabular crystals, often flattened. These crystals combine into rosette-like, fan-shaped, or disordered aggregates on the surface of the host rock.

Geological environment

## Genesis Pandoraite-Ca is a secondary mineral, formed under low-temperature conditions as a result of the oxidation of uranium and vanadium ore minerals. It crystallizes in pores and on the surfaces of cement in sandstones of the Salt Wash Member (Morrison Formation), which are rich in organic matter. ## Mineral Associations This mineral co-occurs with other rare vanadate minerals, such as pandoraite, sherwoodite, doloresite, as well as gypsum and quartz. It occurs on sandstone, which is the host rock. ## Localities The only confirmed locality of Pandoraite-Ca in the world is its type locality: the Pandora mine, located in the La Sal district, San Juan County, Utah, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The collecting appeal of Pandoraite-Ca specimens depends on the richness and aesthetics of the crystal aggregates. Most valued are specimens with numerous, well-formed, lustrous crystals forming dense clusters or distinct rosettes. Contrast with the light background of the host rock (sandstone) and the absence of damage to the delicate crystals are also important. Due to the microscopic nature of the mineral, all specimens fall into the "micromount" category. ## Popular Localities The only source of Pandoraite-Ca specimens is the Pandora mine in Utah, USA. This is the type locality, and all materials available on the collector's market originate from there.

Care and storage

## Cleaning Pandoraite-Ca specimens are extremely delicate and susceptible to mechanical damage. Cleaning is not recommended. If absolutely necessary, compressed air (from a safe distance) can be used to remove loose dust. Any contact with water, chemicals, or tools should be avoided. ## What to Avoid Contact with water and any liquids that could damage both the mineral itself and the host rock (sandstone) must be strictly avoided. The specimen should be protected from vibrations, impacts, abrasion, and sudden temperature changes. Ultrasonic cleaners must not be used. ## Storage Specimens should be stored under stable conditions, in a closed, padded "micromount" box to protect them from dust, moisture, and physical damage. Display should only take place under a microscope.

Sources

IMA Mineral List (CNMNC)