Bearthite
Chemical formula: Ca<sub>2</sub>Al(PO<sub>4</sub>)<sub>2</sub>OH
Bearthite is a rare phosphate mineral, forming small, colorless to pale green crystals, prized by specialized collectors.
Properties
- Mohs hardness
- 5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.22
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identifying bearthite under amateur conditions is very difficult due to the small size of its crystals. Recognition relies on observing the crystal form (small, tabular, often in aggregates), vitreous luster, and occurrence in a specific geological environment. Final confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Distinguishing from Similar Minerals Bearthite can be confused with other rare phosphates or silicates found in similar parageneses, such as lazulite, wagnerite, or some apatites. Distinguishing it from these minerals visually is practically impossible and requires specialized studies. ## Crystal Forms Bearthite crystals are tabular or bladed, flattened parallel to the cleavage plane. They often form fan-shaped, radial, or rosette-like aggregates. They also occur as fine grains within the rock mass.
Geological environment
## Genesis Bearthite is a metamorphic mineral, formed under high-pressure conditions. It forms in aluminum-rich rocks, such as quartzite schists, gneisses, or eclogites. Its formation is associated with regional metamorphism processes, often in the eclogite or glaucophane facies. ## Mineral Associations This mineral co-occurs with other high-pressure minerals. The most common associations include quartz, lazulite, clinozoisite, paragonite, kyanite, staurolite, garnet (almandine), rutile, hematite, and apatite. ## Localities The most important and classic localities for bearthite are in the Western Alps, particularly in the Dora Maira Massif in Italy (type locality) and in the Zermatt-Saas region in Switzerland. It is also known from the Greek island of Sifnos and from several localities in China (e.g., in the Sulu region).
Rarity
Very rare
For collectors
## Quality Criteria The collector's appeal of bearthite primarily depends on the crystal habit and size, which is a rarity. The most prized specimens are those with distinct, sharp crystals forming aesthetic, rosette-like aggregates on a contrasting rock matrix. The intensity of the pale green color, though usually faint, can increase the specimen's value. Due to the microscopic size of the crystals, the quality of the specimen under magnification is crucial. ## Popular Localities The most sought-after specimens by collectors come from the type locality in the Dora Maira Massif in the Cottian Alps of Italy. Specimens from this locality are considered classic and serve as a benchmark for this mineral.
Care and storage
## Cleaning Bearthite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to the small size of the crystals and their fragility, wet cleaning or ultrasonic cleaners are not recommended. ## What to Avoid Avoid contact with acids and other aggressive chemicals that can damage the mineral. It should also be protected from high temperatures and sudden temperature changes. Due to its perfect cleavage, specimens are sensitive to impact and pressure. ## Storage Collectible bearthite specimens, due to their small size and delicacy, are best stored in closed "micromount" boxes, which protect them from dust, mechanical damage, and direct light.