Sabelliite

Chemical formula: Cu²⁺₂Zn²⁺As⁵⁺O₄(OH)₃

Sabelliite is a very rare copper and zinc arsenate, forming characteristic blue, spherical aggregates.

## Characteristics Sabelliite is a hydrated copper and zinc arsenate. It occurs as very small, spherical or hemispherical aggregates with a radial, fibrous internal structure. The individual crystals forming these aggregates are acicular or bladed and rarely exceed 0.2 mm in length. Due to their appearance, sabelliite clusters are sometimes described as "sea urchins" or "brushes" on the host rock. ## Physical Properties Sabelliite crystals exhibit a vitreous luster. The mineral is translucent. Its Mohs hardness is approximately 3, and its density is estimated at 4.25 g/cm³. ## Colors and Varieties Sabelliite has a characteristic, intense color ranging from blue to bluish-green. No varieties are distinguished. ## History and Name The mineral was approved by IMA in 2000. Its name honors Cesare Sabelli (born 1934), an Italian mineralogist and crystallographer from the University of Florence and the National Research Council (CNR), for his contributions to the study of sulfate and borate minerals. ## Uses Sabelliite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals or secondary minerals from oxidation zones.

Properties

Mohs hardness: 4.5
Color: Emerald-green, grass-green
Luster: Adamantine
Streak: Light green
Density: 0
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent
Crystal system: Trigonal

Diagnostic features

## Identification Sabelliite is recognizable by its characteristic mode of occurrence – as small, blue, spherical aggregates with a radial structure. The intense color and co-occurrence with other secondary copper and zinc minerals in oxidation zones are key indicators. ## Distinguishing from Similar Minerals It can be confused with other rare, blue copper arsenates or sulfates, such as ktenasite, linarite, or cyanotrichite. Distinguishing it from ktenasite (which tends to form crusts and coatings rather than spherical aggregates) or cyanotrichite (which has a more silky luster and forms acicular "plushy" coatings) often requires advanced analysis (XRD, EDS) due to visual similarity and small crystal sizes. ## Crystal Forms It forms spherical or hemispherical aggregates composed of very fine, acicular or bladed crystals arranged radially. Single, isolated crystals are extremely rare.

Geological environment

## Genesis Sabelliite is a secondary mineral, forming in the oxidation zones (gossans) of polymetallic deposits rich in copper, zinc, and arsenic. It forms as a result of the weathering of primary ore minerals such as chalcopyrite, sphalerite, and arsenopyrite, under low-temperature and low-pressure conditions. ## Mineral Associations It most commonly co-occurs with other secondary minerals such as anglesite, brochantite, ktenasite, linarite, sphalerite, chalcopyrite, galena, quartz, barite, and gypsum. ## Localities The most important and well-documented localities worldwide include: - Sa Duchessa Mine, Oridda, Domusnovas, Sardinia, Italy (type locality). - Montevecchio Mine, Arbus, Sardinia, Italy. - La Garonne Mine, Le Pradet, Var, France.

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized sabelliite specimens are those with well-formed, clearly defined spherical aggregates of intense blue color, contrasting with a light host rock (e.g., quartz). The size and number of aggregates on the specimen, as well as the absence of damage to the delicate, acicular crystals, are also important. The presence of rare associated minerals can increase the value of a specimen. ## Popular Localities Specimens from the type locality – the Sa Duchessa mine in Sardinia, Italy – are by far the most sought after by collectors. Material from the French La Garonne mine is also highly valued.

Care and storage

## Cleaning Specimens should be cleaned exclusively with compressed air to remove dust. Due to the extreme delicacy of the acicular crystals, any mechanical contact, including with brushes or pressurized water, should be avoided. ## What to Avoid Contact with water, acids, and other chemicals that can damage or dissolve the microscopic crystals must be absolutely avoided. The mineral is sensitive to ultrasound and vibrations. It should not be heated or exposed to prolonged strong light. ## Storage Sabelliite specimens require storage under stable conditions, preferably in a sealed "micromount" box, which protects them from dust, humidity, and mechanical damage. Places with fluctuating temperature and humidity should be avoided.