Isselite

Chemical formula: Cu<sup>2+</sup><sub>6</sub>(S<sup>6+</sup>O<sub>4</sub>)(OH)<sub>10</sub>(H<sub>2</sub>O)<sub>4</sub>·H<sub>2</sub>O

Isselite is a very rare, secondary copper sulfate with a characteristic blue color, forming acicular crystals and radial aggregates.

## Characteristics Isselite is a hydrated copper hydroxyl sulfate, occurring as very small, acicular or capillary crystals. It typically forms small, radial aggregates, rosettes, or spherical clusters of an intense blue color. Individual crystals rarely exceed 1 mm in length and are extremely delicate. Due to its appearance and small size, isselite is a mineral valued mainly by specialized collectors of rare species. ## Physical Properties Isselite crystals exhibit a vitreous luster and are transparent. The Mohs hardness has not been precisely determined, but given its nature and associations with other secondary copper minerals, it can be assumed to be a relatively soft mineral. The density calculated based on the formula and cell parameters is 3.25 g/cm³. ## Colors and Varieties This mineral occurs in a uniform, characteristic shade of blue or light blue. No color or commercial varieties have been distinguished. ## History and Name Isselite was discovered in the Libiola copper mine in Italy and officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2018 (IMA2018-034). Its name honors Arturo Issel (1842–1922), an Italian geologist, paleontologist, and archaeologist, professor at the University of Genoa, who made significant contributions to the geological research of Liguria, the region where the discovery was made. ## Uses Isselite has no industrial applications. Its significance is purely scientific and collectible.

Properties

Luster
Vitreous
Streak
Light blue
Density
3.25
Cleavage
None
Fracture
Uneven
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification Isselite can be recognized by its characteristic form – tiny, acicular crystals forming radial or spherical aggregates. The intense blue color is also a key feature. Due to the microscopic size of the crystals, final identification requires advanced analytical methods such as Raman spectroscopy or X-ray diffraction. ## Distinguishing from similar minerals Isselite can be confused with other secondary, acicular copper sulfates, such as ktenasite, niedermayrite, or devilline. Distinguishing it from these minerals with the naked eye is practically impossible and requires specialized studies. Key differences lie in the crystal structure and precise chemical composition. ## Crystal forms This mineral forms very thin, acicular or capillary crystals, elongated along the [001] axis. These crystals combine into characteristic radial aggregates, fans, rosettes, and spherical clusters.

Geological environment

## Genesis Isselite is a secondary mineral, formed in the oxidation (weathering) zones of copper sulfide deposits. It forms under low-temperature conditions as a result of sulfate-rich waters acting on primary copper minerals. Its formation is associated with the activity of mine waters in old mining workings. ## Mineral associations At the type locality (Libiola mine), isselite occurs in association with other rare secondary minerals, such as chalcanthite, brochantite, antlerite, gypsum, as well as newly discovered minerals like libecciite and niedermayrite. ## Localities The only confirmed occurrence of isselite in the world is its type locality – the Libiola copper mine, located in the municipality of Sestri Levante, Liguria, Italy. This is a historic mine, known for the occurrence of many rare and unique secondary minerals.

Rarity

Very rare

For collectors

## Quality criteria The quality of isselite specimens is primarily assessed based on the richness and aesthetics of the aggregates. Most valued are specimens with well-formed, spherical or radial clusters of intense blue color, contrasting with the rock matrix. The size of these aggregates and the absence of damage to the delicate crystals are also important. The presence of rare associated minerals can further increase the value of the specimen. ## Popular localities The only source of isselite specimens is the Libiola mine in Italy. Material from this locality is highly sought after by collectors specializing in rare minerals and in minerals from specific localities (so-called "locality collectors").

Care and storage

## Cleaning Isselite specimens are extremely delicate and sensitive. Mechanical cleaning is inadvisable and will almost certainly destroy the fragile needles. If absolutely necessary, dust can be attempted to be removed using a stream of compressed air from a very long distance and at minimal pressure. Contact with water, which can dissolve the mineral, should be avoided. ## What to avoid Contact with water, acids, detergents, and all other chemicals must be strictly avoided. The mineral is likely sensitive to high temperatures and direct sunlight, which can lead to its dehydration and color change. It should not be touched, as even the slightest pressure will destroy the crystals. ## Storage Isselite specimens should be stored exclusively in closed, stable "micromount" containers to protect them from dust, moisture, and mechanical damage. They should be kept in a dry place, away from heat and light sources.

Sources

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