Juonniite
Chemical formula: CaMgSc(PO<sub>4</sub>)<sub>2</sub>(OH)·4H<sub>2</sub>O
Juonniite is an extremely rare, hydrated scandium, magnesium, and calcium phosphate, forming small, colorless tabular crystals.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous
- Streak
- White
- Density
- 2.43
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of juonniite is practically only possible using advanced laboratory methods, such as Raman spectroscopy or chemical analysis with an electron microprobe (EDS/WDS). Preliminary identification in a collection is based on the characteristic habit of small, tabular crystals and co-occurrence with other rare phosphates in known localities. ## Distinguishing from Similar Minerals It can be confused with other colorless, microscopic secondary minerals, such as gypsum or other rare phosphates. Definitive differentiation requires chemical analysis, which will show the presence of scandium, magnesium, and phosphorus in appropriate proportions. ## Crystal Forms It forms very small, thin crystals with a tabular or lamellar habit, often flattened. These crystals group into small, radial aggregates, rosettes, or disordered clusters on the surface of other minerals.
Geological environment
## Genesis Juonniite is a secondary mineral, formed in the late stages of granitic pegmatite crystallization. It forms in rock cavities and fissures as a result of hydrothermal processes, which lead to the alteration of previously crystallized minerals, particularly beryl and other phosphates. ## Mineral Associations This mineral occurs in association with other, often rare, pegmatitic minerals. At its type locality (Juonni quarry), it was found in association with albite, quartz, beryl, eudialyte, as well as other phosphates such as viitaniemiite, väyrynenite, and morinite. ## Localities The only confirmed and described occurrence of juonniite in the world is its type locality: the Juonni quarry in the municipality of Salla, in the Lapland region of Finland.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of juonniite specimens is primarily assessed based on the richness and aesthetics of the microscopic crystal aggregates. The most desirable specimens are those with clearly formed, undamaged rosettes or radial clusters of crystals, contrasting well with the surrounding rock. The size of individual crystals, although always microscopic, is also important – the larger and better-formed they are, the more valuable the specimen. Association with other rare minerals from this locality is also key.
Care and storage
## Cleaning Due to the extreme fragility and small size of the crystals, mechanical cleaning is not recommended and can lead to damage to the specimen. If cleaning is absolutely necessary, compressed air can be carefully used from a safe distance to remove loose dust particles. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and all forms of mechanical cleaning (brushes, cloths). The mineral is soft and brittle, and may also be sensitive to changes in humidity and temperature. ## Storage Juonniite specimens should be stored exclusively in specialized collector's boxes (so-called "micromount boxes") that protect them from physical damage, dust, and environmental changes. Avoid exposure to direct sunlight.