Markeyite

Chemical formula: Ca<sub>9</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>4</sub>(CO<sub>3</sub>)<sub>13</sub>·28H<sub>2</sub>O

Markeyite is a very rare, secondary uranyl mineral, forming bright yellow, fluorescent coatings and aggregates of fine crystals.

## Characteristics Markeyite is a hydrated calcium uranyl carbonate, occurring as microscopic, bladed or acicular crystals. It forms delicate, fibrous aggregates, rosettes, and thin coatings and efflorescences on host rocks. Due to the small size of its crystals, its macroscopic features are difficult to observe, and most specimens appear as powdery or chalky masses. ## Physical Properties Markeyite crystals are extremely small and brittle. The mineral exhibits strong, bright green fluorescence under shortwave ultraviolet light (UV-SW) and somewhat weaker fluorescence under longwave (UV-LW). It is a strongly radioactive mineral. ## Colors and Varieties Markeyite occurs in shades from pale yellow to bright yellow, sometimes with a greenish tint. No varieties have been distinguished. ## History and Name The mineral was named in honor of Jack R. Markey (born 1943), an American mineral collector from Mesa County, Colorado, who specialized in uranium minerals and was the first to find specimens of this mineral. It was approved as a new mineral species by the IMA in 2017 (IMA2017-054), and its description was published in 2018. The type locality is the Markey Mine in Red Canyon, San Juan County, Utah, USA. ## Uses Markeyite, due to its rarity, small size, and strong radioactivity, is of purely scientific and collector interest. It is sought after by specialized collectors of uranium minerals.

Properties

Mohs hardness
2
Luster
Pearly
Streak
Pale yellow
Density
2.53
Cleavage
Perfect on {001}
Fracture
Micaceous
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification The key diagnostic feature of markeyite is its very strong, bright green fluorescence under UV light (both shortwave and longwave). It occurs in characteristic, chalky white or bright yellow, powdery coatings and aggregates of fine, bladed crystals. However, identification most often requires advanced research methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Markeyite can be confused with many other secondary uranyl minerals of similar color and habit, such as andersonite, liebigite, schröckingerite, bayleyite, or fontanite. Andersonite and liebigite exhibit similar green or blue-green fluorescence. Definitive differentiation is almost exclusively possible based on chemical and crystallographic analysis. ## Crystal Forms Markeyite forms very small, bladed crystals, elongated along [010] and flattened parallel to {001}. These crystals aggregate into spherical or hemispherical masses, rosettes, and also form thin coatings and efflorescences.

Geological environment

## Genesis Markeyite is a secondary uranium mineral, forming in the oxidation zones of uranium deposits. It forms as a result of carbonate-rich waters acting on primary uranium minerals. It forms under low-temperature conditions, most often as a post-mining product on tunnel walls and in mine workings, where it crystallizes from seeping waters. ## Mineral Associations This mineral co-occurs with other secondary uranium minerals. At the type locality (Markey Mine, Utah), it was found in association with gypsum, schröckingerite, andersonite, liebigite, bayleyite, and boltwoodite. ## Localities Confirmed occurrences of markeyite are extremely rare. Besides the type locality at the Markey Mine in San Juan County, Utah (USA), it has been identified in several other locations on the Colorado Plateau, including the Delta and Blue Lizard mines in the same county. It is also known from the Svornost Mine in Jáchymov, Czech Republic.

Rarity

Very rare

For collectors

## Quality Criteria The collector appeal of a specimen depends on the richness and visibility of markeyite coatings on the rock matrix. Specimens with clearly formed, though still microscopic, crystal aggregates, rather than just dusty coatings, are most valued. The intensity of fluorescence under UV light is also important. A contrasting rock matrix can enhance the aesthetic value of the specimen. ## Popular Localities By far the most known and valued specimens come from the type locality – the Markey Mine in Red Canyon, San Juan County, Utah, USA. Specimens from this locality are considered exemplary for this mineral.

Care and storage

## Cleaning Markeyite specimens are generally not cleaned. Any attempts at mechanical or chemical cleaning can irreversibly destroy the delicate crystals. Only very careful removal of loose contaminants with a soft brush or a photographic air blower is permissible. ## What to Avoid Contact with water and chemicals must be strictly avoided. The mineral is sensitive to changes in humidity and temperature. As a secondary mineral, it is unstable under conditions other than those in which it formed. It should be protected from direct sunlight, which can cause dehydration and disintegration. Due to strong radioactivity, direct contact, inhalation of dust, and storage in areas of permanent human habitation should be avoided. ## Storage Specimens should be stored in airtight, sealed containers (e.g., "perky boxes") to stabilize humidity and protect delicate crystals from damage. Containers should be appropriately labeled with a radioactivity symbol and stored in specialized display cases or cabinets, away from other radiation-sensitive minerals.

External references

Sources

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