Arhbarite
Chemical formula: Cu<sup>2+</sup><sub>2</sub>MgAs<sup>5+</sup>O<sub>4</sub>(OH)<sub>3</sub>
Arhbarite is a rare copper and magnesium arsenate, forming characteristic blue-green spherical aggregates.
Properties
- Mohs hardness
- 3
- Luster
- Vitreous
- Streak
- Light blue
- Density
- 4.29
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Characteristic features of arhbarite include its vivid blue-green color, spherical or hemispherical aggregates with a radial-fibrous structure, and occurrence in the oxidation zones of ore deposits. Due to the small size of the crystals, definitive identification requires advanced analytical methods such as Raman spectroscopy or chemical analysis (EDS). ## Distinguishing from Similar Minerals Arhbarite can be confused with other secondary copper minerals of similar color and habit, such as aurichalcite, rosasite, cyanotrichite, or brochantite. Distinguishing it "with the naked eye" is practically impossible. Chemical composition analysis is key – the presence of magnesium and arsenic, along with the absence of zinc or sulfur, is decisive. ## Crystal Forms Arhbarite forms very fine, bladed or acicular crystals that combine into radial, spherical (spherulitic) or hemispherical aggregates. Individual, well-formed crystals are extremely rare and microscopic in size.
Geological environment
## Genesis Arhbarite is a secondary mineral, formed in the oxidation (weathering) zones of hydrothermal polymetallic ore deposits rich in arsenic and copper. It forms as a result of reactions between solutions containing copper and arsenate ions with magnesium-rich rocks, such as dolomite. ## Mineral Associations This mineral co-occurs with other secondary arsenate and sulfate minerals. In the type locality (Arhbar mine), it was found in association with geminite, oswaldpeetersite, erythrite, annabergite, gypsum, dolomite, and quartz. ## Localities The only confirmed and described occurrence of arhbarite in the world is its type locality – the Arhbar mine, in the Bou Azzer district, Drâa-Tafilalet region, Morocco.
Rarity
Very rare
For collectors
## Quality Criteria The most prized arhbarite specimens are those with numerous, well-formed, spherical aggregates of intense blue-green color, contrasting with a light host rock (most often dolomite). The absence of damage to the delicate spherulites and aesthetic arrangement on the matrix are important. Due to the microscopic nature of the mineral, specimens are primarily evaluated based on their richness and aesthetics on a "micromount" scale. ## Popular Localities The only source of arhbarite specimens is the Arhbar mine in Morocco. All samples available on the collector's market come from this single location.
Care and storage
## Cleaning Arhbarite specimens are extremely delicate and susceptible to mechanical damage. Cleaning should be kept to an absolute minimum. If necessary, compressed air (from a safe distance) can be used to remove loose dust. Avoid contact with water and any chemicals. ## What to Avoid Arhbarite, as an arsenate, is potentially toxic – avoid inhaling dust and wash hands after any contact with the mineral. Protect it from moisture, acids, detergents, and high temperatures. Brittle aggregates are easily scratched or crushed. ## Storage Specimens should be stored in closed, stable containers (e.g., "micromount" type) to protect them from dust, moisture, and mechanical damage. Do not expose them to direct sunlight, which can cause discoloration.