Senegalite
Chemical formula: Al<sub>2</sub>PO<sub>4</sub>(OH)<sub>3</sub>·H<sub>2</sub>O
Senegalite is a rare hydrated aluminum phosphate, forming characteristic, bright green or yellowish crystals with a platy or short prismatic habit.
Properties
- Mohs hardness
- 5.5
- Luster
- Vitreous, Resinous
- Streak
- White
- Density
- 2.53
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Senegalite can be identified by its characteristic bright green color, platy crystal habit, and occurrence in radial aggregates. Its vitreous luster and relatively high hardness (for a phosphate) are also helpful features. ## Distinguishing from Similar Minerals It can be confused with other secondary green phosphates, such as variscite or wavellite. It differs from variscite by its higher hardness and different crystal form (variscite rarely forms distinct crystals). From wavellite, which also forms radial aggregates, senegalite differs in the habit of individual crystals – wavellite is acicular, while senegalite forms platy crystals. ## Crystal Forms Senegalite crystals are orthorhombic, most often platy, flattened parallel to {010}, or short prismatic. They often occur as fan-shaped or spherulitic aggregates, as well as rosettes and crusts.
Geological environment
## Genesis Senegalite is a secondary phosphate mineral that forms in the oxidation zone of phosphorite deposits. It forms as a result of weathering and alteration of aluminum- and phosphorus-rich minerals under low temperature and pressure conditions. ## Mineral Associations This mineral co-occurs with other secondary phosphates, such as wavellite, crandallite, and turquoise. At its type locality in Senegal, it was found in association with wavellite and crandallite. ## Localities The most important and type locality for senegalite is the Kouroudiako phosphorite deposit in the Tambacounda region of Senegal. This is the only confirmed and well-documented locality for this mineral in the world, making it extremely rare.
Rarity
Very rare
For collectors
## Quality Criteria Specimens with well-formed, sharp, and transparent crystals of intense green color are most valued by collectors. Aesthetically formed, radial aggregates on a contrasting rock matrix enhance their attractiveness. Due to the small size of its crystals, senegalite is a popular subject in "micromount" collections. ## Popular Localities The only source of collector specimens is the type locality – Kouroudiako in Senegal. All specimens available on the market originate from this single location.
Care and storage
## Cleaning Senegalite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Always thoroughly dry the specimen at room temperature. ## What to Avoid Avoid contact with acids and other chemicals that can damage the crystal surface. The mineral is sensitive to high temperatures, which can lead to dehydration and destruction. It should also not be cleaned in ultrasonic cleaners. ## Storage Collector specimens of senegalite, especially those in the form of micromounts, are best stored in closed, padded boxes to protect them from dust and mechanical damage. Avoid exposure to direct sunlight and sudden temperature changes.