Bonattite

Chemical formula: Cu<sup>2+</sup>S<sup>6+</sup>O<sub>4</sub>·3H<sub>2</sub>O

A rare, secondary copper sulfate, forming pale blue efflorescences and crusts in dry mine environments.

## Characteristics Bonattite is a hydrated copper sulfate, most commonly occurring as pale blue or bluish-green, earthy or powdery coatings and crusts. It rarely forms microscopic, lath-like crystals. It is a secondary mineral, formed under specific, dry conditions, often as a product of dehydration of chalcanthite. ## Physical Properties This mineral is very soft, with a Mohs hardness of about 3. Its luster is described as vitreous, although in the case of earthy aggregates, it becomes dull. It is translucent to opaque. Due to its structure and chemical composition, it is soluble in water. ## Colors and Varieties Bonattite occurs in shades from light blue and sky blue to bluish-green. Its color is usually paler and less intense than that of chalcanthite. No color or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1957, honors Stefano Bonatti (1902–1968), a professor of mineralogy at the University of Pisa, Italy, who first described this mineral. It was discovered in the Riphah mine in Tuscany, Italy. ## Uses Bonattite has no industrial application. Its significance is purely scientific and as a collector's item, as a rare member of the copper sulfate group.

Properties

Mohs hardness
3
Luster
Vitreous
Streak
Pale blue
Density
2.55
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of bonattite include its pale blue color, occurrence as powdery or earthy crusts, and its specific formation environment – dry mine workings. A key, though destructive, diagnostic feature is its solubility in water. ## Distinguishing from Similar Minerals Bonattite is most often confused with **chalcanthite**. However, chalcanthite has a much more intense, deep blue color and forms larger, better-developed crystals. It also differs in its higher degree of hydration (five water molecules in the structure compared to three in bonattite). Final differentiation of these minerals often requires laboratory analyses (e.g., XRD). ## Crystal Forms Well-formed crystals are extremely rare and appear as microscopic, tabular or lath-like forms. Typically, bonattite forms very fine-grained aggregates, crusts, coatings, and efflorescences.

Geological environment

## Genesis Bonattite is a secondary mineral, forming in the oxidation zones of copper ore deposits. Its formation is favored by dry, arid climates or well-ventilated, dry parts of underground mine workings. It forms as a result of partial dehydration of the more hydrated copper sulfate – chalcanthite. ## Mineral Associations It most commonly co-occurs with other secondary copper sulfates, such as chalcanthite and poitevinite, as well as with gypsum, chalcopyrite, pickeringite, and other minerals of the oxidation zone. ## Localities Important localities worldwide include: the Riphah mine in Tuscany (Italy), where it was discovered; Vulcano Island (Italy); the large copper deposits in Chuquicamata (Chile); and the San Manuel mine in Arizona (USA).

Rarity

Rare

For collectors

## Quality Criteria For such a rare mineral, the main criterion for value is reliable confirmation of its identity and accurate locality documentation. Specimens are not evaluated for aesthetics, which are usually low. The most desirable samples are those with a well-defined mineral association, originating from a type locality (località classica). ## Popular Localities The most prized specimens by collectors come from classic localities, such as the mines in Tuscany, Italy, and from the dry regions of Chile (Chuquicamata), where rich aggregates of secondary sulfates are found.

Care and storage

## Cleaning Bonattite **must not be wet cleaned**. It is soluble in water, and contact with it will destroy the specimen. Only very careful removal of dust with a soft, dry brush or a photographic blower is permissible. ## What to Avoid Contact with water, water vapor, and high humidity must be strictly avoided. In a humid environment, bonattite can spontaneously rehydrate, transforming into chalcanthite. It should also be protected from high temperatures, which can accelerate further dehydration. ## Storage Bonattite specimens require storage in conditions of controlled, low humidity. The best solution is a sealed, airtight container (e.g., a "perky box") with a desiccant, such as silica gel, placed inside.

Sources

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