Rossite
Chemical formula: Ca(V<sup>5+</sup>O<sub>3</sub>)<sub>2</sub>·4H<sub>2</sub>O
Rossite is a rare, hydrated calcium vanadate, forming bright yellow, unstable coatings and efflorescences on uranium-vanadium rocks.
Properties
- Mohs hardness
- 1-2
- Luster
- Vitreous, Silky
- Streak
- Light yellow
- Density
- 2.45
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification Rossite is identified by its characteristic bright yellow color, very low hardness, and mode of occurrence – it forms soft, earthy, or fibrous coatings and efflorescences. A key feature is its instability in dry air, where it quickly whitens and dulls, transforming into metarossite. It reacts violently, dissolving in water. ## Distinguishing from Similar Minerals It can be confused with other secondary vanadium minerals, such as carnotite, tyuyamunite, or pascoite. Carnotite and tyuyamunite are harder and do not dissolve as easily in water. Pascoite usually has a more orange hue. Final differentiation from the very similar metarossite requires chemical analysis (XRD), although a fresh, vitreous appearance indicates rossite. ## Crystal Forms Macroscopic crystals are not known. It occurs as microscopic, acicular or lamellar crystals forming fibrous, earthy, felted aggregates, as well as coatings and efflorescences.
Geological environment
## Genesis Rossite is a secondary mineral that crystallizes from vanadium-rich waters under low-temperature conditions. It forms in the oxidation (weathering) zone of uranium-vanadium sandstone deposits, often in arid climates. It forms as a product of dehydration of other vanadates or directly precipitates on mine workings walls. ## Mineral Associations It most often co-occurs with metarossite (into which it transforms), as well as with other vanadates such as pascoite, hewettite, and carnotite. Gypsum and clay minerals also accompany it. ## Localities The most important localities worldwide, from which the best-known specimens originate, are in the USA, in the Colorado Plateau region (Colorado, Utah, Arizona states). The type locality is Bull Pen Canyon in San Miguel County, Colorado. It has also been found in mines in Paradox Valley (Montrose County, Colorado) and in the Thompsons area in Grand County, Utah.
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of rossite depends primarily on the intensity and purity of its bright yellow color and the abundance of the coating on the host rock. The most valued specimens are those that were properly secured immediately after extraction and have retained their original, vitreous luster, without transitioning to dull metarossite. Due to the microscopic nature of the crystals, their form is not a key criterion for visual assessment. ## Popular Localities The vast majority of collector specimens come from classic localities on the Colorado Plateau in the USA, especially from mines in San Miguel and Montrose counties in Colorado.
Care and storage
## Cleaning Rossite is extremely delicate and water-soluble. It should not be cleaned wet. Any contaminants, such as dust, can only be removed using a soft brush or a stream of compressed air from a distance and with low force. ## What to Avoid Contact with water and other liquids, which will dissolve it, must be absolutely avoided. The mineral is very unstable in dry air – it quickly dehydrates to metarossite, losing its original appearance and structure. It should be protected from changes in humidity, high temperatures, and direct sunlight. It is very soft and brittle, susceptible to the slightest mechanical damage. ## Storage Rossite specimens must be stored in sealed, airtight containers (e.g., "perky box" type or vials) to maintain stable ambient humidity and prevent dehydration. The container should protect the specimen from shocks and damage. Store in a dark and cool place.