Afmite
Chemical formula: Al<sub>3</sub>(OH)<sub>4</sub>(H<sub>2</sub>O)<sub>3</sub>(PO<sub>4</sub>)(PO<sub>3</sub>OH)·H<sub>2</sub>O
Afmite is a very rare, hydrated aluminum phosphate, forming colorless or white, tabular crystals aggregated into spherical forms.
Properties
- Mohs hardness
- 2
- Luster
- Pearly, Vitreous
- Streak
- White
- Density
- 2.29
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification The diagnostic feature of afmite is its unique mode of occurrence: spherical or hemispherical aggregates and rosettes, composed of tiny, colorless, tabular crystals with a pearly luster on cleavage surfaces. Its extreme rarity and occurrence in a specific geological environment are also crucial. ## Distinguishing from Similar Minerals Afmite can be confused with other white, secondary phosphates with radial aggregates, such as wavellite or matulaite. Wavellite typically forms larger, more distinct spherulites. Matulaite has a very similar appearance but a different crystal structure and chemical composition. Reliable distinction of these minerals is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Crystal Forms Crystals are thin-tabular, flattened parallel to the {010} cleavage plane and elongated along the [100] crystallographic axis. They form fan-shaped, rosette-like, and spherical aggregates up to approximately 1 mm in diameter.
Geological environment
## Genesis Afmite is a secondary mineral. It forms as a result of weathering and alteration of primary phosphate minerals (mainly amblygonite) within phosphate-rich lenses occurring in metamorphic rocks (schists). ## Mineral Associations At the type locality, afmite coexists with other, often rare, secondary phosphates, such as matulaite, tinticite, wavellite, variscite, and minerals from the crandallite group. ## Localities The only well-documented and most important occurrence of afmite in the world is the Fumade quarry, located near Castelnau-de-Brassac in the Tarn department, France. It is a mineral with an extremely limited range of occurrence.
Rarity
Very rare
For collectors
## Quality Criteria The quality of afmite specimens, being a micromount mineral, is assessed based on several criteria. Specimens with well-formed, sharp, and distinct spherical aggregates or rosettes are most highly valued. The abundance of the mineral on the rock matrix and the aesthetic composition with other rare associated minerals are also important. The purity (lack of damage) and definition of the crystals forming the aggregates significantly increase their collectible value. ## Popular Localities The only source of collectible specimens is the type locality – the Fumade quarry in France. Material from this locality is highly prized by specialists and collectors of microscopic minerals.
Care and storage
## Cleaning Afmite is extremely delicate and soft. It should be handled with utmost care. For dust removal, it is best to use a photographic air blower or a very soft brush. Washing in water is not recommended; if absolutely necessary, use distilled water and dry the specimen as quickly as possible, avoiding heating. ## What to Avoid Avoid any mechanical stress, friction, and contact with hard objects. The mineral is sensitive to chemicals, so no acids or detergents should be used. Ultrasonic cleaners will cause its immediate destruction. High temperatures should also be avoided, as they can lead to dehydration and structural breakdown. ## Storage Afmite specimens should only be stored in specialized, padded micromount boxes that protect them from dust, shocks, and mechanical damage.