Kristekite
Chemical formula: Cu<sup>2+</sup><sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>(U<sup>6+</sup>O<sub>2</sub>)(Se<sup>4+</sup>O<sub>3</sub>)<sub>3</sub>·4H<sub>2</sub>O
A very rare, radioactive hydrated copper uranyl selenite, known from the uranium deposit in Příbram, Czech Republic.
Properties
- Mohs hardness
- 2-3
- Color
- yellowish-green
- Streak
- pale green
- Density
- 3.729
- Cleavage
- excellent on {001}, distinct on {100}
- Fracture
- Sub-Conchoidal
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Visual identification is very difficult. The yellow-green color and pale green streak combined with strong radioactivity may suggest a uranyl mineral, but definitive identification of křístekite requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS), confirming the presence of copper, selenium, and uranium. ## Distinction from similar minerals It can be confused with many other secondary uranium minerals, especially with other copper uranyl selenites, sulfates, or phosphates, which often co-occur under similar conditions and have a similar yellow-green or green color. ## Crystal habits It crystallizes in the monoclinic system. It forms small, transparent crystals exhibiting perfect cleavage along the {001} plane.
Geological environment
## Origin It is a secondary mineral forming in the oxidation zones of uranium deposits rich in selenium and copper. It forms as a result of weathering of primary uranium minerals (such as uraninite) and selenides under low-temperature conditions. ## Mineral associations It co-occurs with other secondary uranium and selenium minerals typical of the oxidation zone of uranium deposits. ## Localities The most important and confirmed locality of this mineral is its type locality: uranium mine No. 11A (shaft 11A) in Bytíz, in the Příbram region (Czech Republic).
Rarity
Extremely rare
For collectors
## Quality criteria Due to its extreme rarity, every analytically confirmed specimen of křístekite is highly valued. Attractiveness is determined by crystal size and development, although these are usually microscopic specimens requiring observation under a loupe or microscope (micromounts). ## Notable localities The only source of specimens in systematic collections is the mineral's type locality - Příbram, Czech Republic (Bytíz mine).
Care and storage
## Cleaning Specimens should not be washed in water or any chemical solutions due to the solubility and delicate nature of hydrated selenites. Only very careful blowing with low-pressure compressed air is permissible to remove dust. ## What to avoid Moisture must be strictly avoided as it can lead to decomposition of the mineral, as well as direct sunlight and elevated temperatures, which can cause dehydration (loss of water of crystallization). Direct physical contact should be avoided due to low hardness, toxicity (content of copper and selenium), and radioactivity. ## Storage It requires storage in airtight, transparent containers (e.g., micromount boxes) protecting against dust and humidity changes. Due to radioactivity, specimens should be kept in well-ventilated rooms, away from continuously occupied areas, in accordance with safety guidelines for uranium minerals.