Montetrisaite

Chemical formula: Cu²⁺₆(S⁶⁺O₄)(OH)₁₀·2H₂O

Montetrisaite is a very rare, secondary copper mineral with a characteristic blue color, occurring as microscopic, bladed crystals.

## Characteristics Montetrisaite is a hydrated copper hydroxide sulfate, forming extremely small, bladed or acicular crystals that rarely exceed 0.2 mm in length. They typically occur as radial aggregates, rosettes, or tangled, felt-like masses. Due to the microscopic size of the crystals, its visual features are difficult to observe without magnification. ## Physical Properties Montetrisaite crystals exhibit a vitreous luster. Hardness and density have not been precisely measured due to the small size and rarity of the material. It is a transparent mineral. ## Colors and Varieties This mineral is characterized by a uniform, blue or blue-green color. No varieties have been distinguished. ## History and Name The name montetrisaite comes from its discovery locality – the Montetrisa mine in Livorno province, Italy. It was approved as a new mineral by the International Mineralogical Association (IMA) in 1989. It was described by Italian mineralogists Cesare Tasselli, Pierfranco Lattanzi, and Marco Benvenuti. ## Uses Montetrisaite has no industrial application. It is of purely scientific and collector's interest, being a coveted item for collectors specializing in microminerals and rare specimens from specific localities.

Properties

Mohs hardness
2-3
Color
Blue
Luster
Vitreous
Streak
Light blue
Density
0
Cleavage
{001}
Fracture
Conchoidal
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of montetrisaite is based on its characteristic form – tiny, acicular or bladed crystals forming radial aggregates. Its blue color, co-occurrence with other secondary copper minerals, and locality are also key. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Montetrisaite can be confused with other secondary, acicular copper sulfates, such as brochantite, linarite, or ktenasite. Distinguishing it with the "naked eye" or under a microscope is practically impossible without chemical analysis. A key clue is the mineral association at a given locality. ## Crystal Forms It forms elongated, bladed or acicular crystals, flattened parallel to the {100} plane. These crystals combine into radial, stellate aggregates or chaotic, tangled masses.

Geological environment

## Genesis Montetrisaite is a secondary mineral, forming in the oxidation zones (gossans) of sulfide deposits rich in copper. It forms as a result of the weathering of primary copper minerals in the presence of sulfate-rich waters. ## Mineral Associations It most commonly co-occurs with other secondary minerals, such as brochantite, spangolite, chalcanthite, gypsum, as well as tennantite-(Fe) and pyrite. ## Localities It is an extremely rare mineral, known from only a few localities worldwide. Besides the type locality – the Montetrisa mine in Tuscany (Italy) – its presence has also been reported in the Clara mine in the Black Forest (Germany) and in mines in the Atacama region (Chile).

Rarity

Extremely rare

For collectors

## Quality Criteria As a micromineral, the collector's value of montetrisaite primarily depends on the richness and aesthetics of the crystal aggregates on the rock matrix. Specimens with clearly formed, radial clusters of intense blue color, contrasting with the substrate, are most highly prized. Confirmation of the mineral's identification is also important. ## Popular Localities The most classic and sought-after specimens come from the type locality, the Montetrisa mine in Italy. Specimens from the Clara mine in Germany are also well-known in collecting circles.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Any contact with water, even distilled, or other chemicals is highly risky and can destroy the delicate crystals. ## What to Avoid Contact with water and all chemical agents must be strictly avoided. The crystals are extremely fragile and sensitive to mechanical shock. They should not be heated or exposed to prolonged sunlight. ## Storage Montetrisaite specimens, as microminerals, should be stored exclusively in specialized, sealed "micromount" boxes. This protects them from dust, mechanical damage, and sudden changes in humidity.

External references

Sources

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