Pseudomarkeyite
Chemical formula: Ca₈(U⁶⁺O₂)₄(CO₃)₁₂(H₂O)₁₈·3H₂O
Pseudomarkeyite is a rare, secondary uranyl mineral, forming microscopic, yellow crystals and coatings, closely related to markeyite.
Properties
- Mohs hardness
- 1
- Color
- Pale green yellow
- Luster
- Vitreous
- Streak
- White
- Density
- 2.88
- Cleavage
- Three cleavages: <mi>{10_1}</mi> very easy, {010} good, {100} fair
- Fracture
- Step-Like
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Key diagnostic features include its bright yellow color, the form of small, platy crystals forming radial aggregates, and strong green fluorescence under UV light. Identification requires the use of a stereomicroscope. Final confirmation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Pseudomarkeyite is visually almost identical to markeyite. It differs from it by a subtly lower water content in its crystal structure, which translates into a slightly different X-ray diffraction pattern. It can also be confused with other secondary uranyl minerals of similar color and habit, such as andersonite, liebigite, or bayleyite. Differentiation in the field or without specialized equipment is practically impossible. ## Crystal Forms Crystals are elongated, platy, with a rhombic cross-section. They usually occur as radial or stellar aggregates, as well as dispersed acicular crystals and coatings on the rock surface.
Geological environment
## Genesis Pseudomarkeyite is a secondary uranium mineral, formed in the oxidation zones of uranium deposits. It forms as a result of carbonate-rich waters acting on primary uranium minerals, such as uraninite. It forms under conditions of low temperature and humidity, often as a dehydration product of markeyite in a dry environment, e.g., in mine workings. ## Mineral Associations It most often co-occurs with markeyite, from which it directly forms. It is also accompanied by other secondary uranium minerals, such as uraninite, gypsum, andersonite, liebigite, bayleyite, schröckingerite, and uranophane. ## Localities The most important and type locality (localitas typica) is the Markey mine in Red Canyon, White Canyon district, San Juan County, Utah, USA. It has also been identified in other uranium mines in the same region.
Rarity
Very rare
For collectors
## Quality Criteria For collectors, the abundance and aesthetics of crystal aggregates on the rock matrix are most important. Specimens with well-formed, radial rosettes of intense yellow color, contrasting with the dark host rock, are most valued. Association with other rare uranium minerals is also important. ## Popular Localities The only source of well-formed collector specimens is its discovery region - the mines in the White Canyon district in Utah, USA, and especially the Markey mine.
Care and storage
## Cleaning Specimens should not be wet cleaned. Dust can only be removed with a soft brush or a photographic air blower. Avoid skin contact and inhalation of dust due to radioactivity. ## What to Avoid Contact with water and chemicals, which can dissolve or damage delicate crystals, must be strictly avoided. The mineral is sensitive to changes in humidity and temperature. It should not be heated. Due to its uranium content, appropriate safety precautions should be taken. ## Storage Specimens should be stored in closed, airtight containers (e.g., "perky boxes") to protect them from mechanical damage, dust, and humidity changes. Store away from other minerals that may be sensitive to radiation. It is recommended to store in a place inaccessible to children and pets, with appropriate radioactive labeling.