Penikisite
Chemical formula: BaMg<sub>2</sub>Al<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>(OH)<sub>3</sub>
Penikisite is a very rare phosphate mineral, forming small, colorless to light blue monoclinic crystals.
Properties
- Mohs hardness
- 4
- Luster
- Vitreous
- Streak
- White
- Density
- 3.85
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Penikisite is difficult to identify visually without magnification. Under a microscope, it is recognized by its characteristic small, bladed crystals grouped into radial or rosette-like aggregates. The light blue color, if present, is a helpful clue. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Distinguishing from Similar Minerals It can be confused with other rare phosphates from the same locality, such as kulanite, bjarebyite, or satterlyite. Distinguishing it from these is practically impossible without specialized tests. Penikisite is a monoclinic dimorph of hexagonal penikisite-(Y). ## Crystal Forms It forms elongated, bladed crystals with a rhombic cross-section, often flattened. These crystals group into radial aggregates, rosettes, or form chaotic clusters on the surface of the host rock.
Geological environment
## Genesis Penikisite forms in complex granitic pegmatites or in hydrothermal veins cutting through phosphorus-rich sediments, such as sideritic iron clays. It is a secondary mineral, crystallizing in the late stage of low-temperature hydrothermal processes. ## Mineral Associations At the type locality (Rapid Creek, Canada), it co-occurs with quartz, kulanite, satterlyite, lazulite, wardite, apatite, and goethite. ## Localities The most important and practically sole source of well-formed penikisite specimens is its type locality in the Rapid Creek and Big Fish River area of the Northwest Territories, Canada. This is a world-renowned site for rare phosphate minerals.
Rarity
Very rare
For collectors
## Quality Criteria The quality of penikisite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates. The most valued specimens are those with numerous, well-formed, radial rosettes of a distinct, light blue color, contrasting with the darker host rock. The size of individual crystals, although always microscopic, also affects the value. ## Popular Localities The only popular and valued locality among collectors is the Rapid Creek area in Canada. Specimens from this locality are the standard for this mineral.
Care and storage
## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to the size and fragility of the crystals, contact with water and brushes, which could damage them or wash them out of the matrix, should be avoided. ## What to Avoid All chemicals, especially acids, which can react with phosphates, should be avoided. Ultrasonic and mechanical cleaning should be avoided. Protect from high temperatures and sudden temperature changes. ## Storage Penikisite specimens, as microminerals, should be stored in specialized "micromount" boxes or in sealed display cases, protecting them from dust and mechanical damage. Exposure to direct sunlight should be avoided, although there is no evidence of fading.