Larisaite
Chemical formula: Na(H₃O)(U⁶⁺O₂)₃(Se⁴⁺O₃)₂O₂(H₂O)₃·H₂O
Larisaite is a very rare, radioactive uranyl and selenium mineral, forming microscopic, yellow, platy crystals.
Properties
- Mohs hardness
- 1
- Color
- Canary- yellow
- Luster
- Vitreous
- Streak
- Yellow
- Density
- 0
- Cleavage
- On (010)
- Fracture
- Irregular/Uneven
- Transparency
- Transparent,Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identifying larisaite in the field is practically impossible without specialized equipment. Identification relies on chemical (EDS) and X-ray (XRD) analysis. In a collection, it can be identified by its bright yellow color, characteristic form of microscopic, platy crystals forming aggregates, and strong radioactivity. ## Distinguishing from Similar Minerals Larisaite can be confused with many other yellow secondary uranium minerals, such as autunite, carnotite, or tyuyamunite. Differentiation requires advanced analytical methods. The presence of selenium in its chemical composition is key, distinguishing it from many more common uranyl minerals. ## Crystal Forms It forms very small, thin, platy crystals with rectangular or bladed outlines. These crystals often combine into radial or rosette-like aggregates, and also form thin coatings and crusts.
Geological environment
## Genesis Larisaite is a secondary mineral, forming in the oxidation zones of uranium deposits located in sedimentary rocks (sandstones). It forms as a result of the weathering of primary uranium minerals (uraninite) in the presence of selenium-rich solutions. ## Mineral Associations This mineral co-occurs with other secondary uranium and selenium minerals. At its type locality, it was found in association with gypsum, quartz, and other uranyl selenites, such as guilleminite and demesmaekerite. ## Localities The only confirmed occurrence of larisaite in the world is its type locality – the Little Eva uranium deposit, Yellow Cat district, Grand County, Utah, USA.
Rarity
Extremely rare
For collectors
## Quality Criteria As a microscopic mineral, larisaite is valued primarily for the mere confirmation of its presence on a specimen. Samples on which well-formed, even if very small, crystalline aggregates are visible, clearly contrasting in color with the host rock, are most highly rated. The abundance of coatings and association with other rare uranium minerals also increase the value of the specimen. ## Popular Localities The only source of specimens is the Little Eva mine in Utah, USA. Material from this locality is extremely difficult to obtain and appears on the collector's market sporadically.
Care and storage
## Cleaning This mineral is extremely rare and brittle, and mechanical cleaning is not recommended. It usually occurs as microscopic coatings that do not require cleaning. If necessary, compressed air can be used to remove dust. ## What to Avoid Contact with water and chemicals, which can dissolve or damage the delicate crystals, must be absolutely avoided. As a secondary mineral, it is unstable in humid environments. Due to radioactivity, direct skin contact, inhalation of dust, and storage in areas of permanent human presence should be avoided. ## Storage Larisaite specimens must be stored in sealed, lead-lined containers designed for radioactive minerals, away from other radiation-sensitive minerals. It is best to keep them in a dry place, in specialized "perky box" containers, to protect them from mechanical damage.