Devilline

Chemical formula: CaCu<sup>2+</sup><sub>4</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>·3H<sub>2</sub>O

Devilline is a rare secondary mineral from the sulfate group, forming characteristic rosette-like aggregates of tiny, acicular crystals with an intensely blue-green color.

## Characteristics Devilline is a hydrated calcium and copper sulfate, occurring in the oxidation zones of copper ore deposits. It forms very characteristic, thin, tabular or bladed crystals, which almost always occur in radial, spherical, or rosette-like aggregates. Individual crystals are usually very small, rarely exceeding 1-2 mm, but their aggregates can form striking, velvety or druzy coatings on the host rock. ## Physical Properties Devilline crystals are very soft and brittle, with a hardness of only 2.5 on the Mohs scale. They exhibit perfect, unidirectional cleavage, which is visible on larger crystals. The luster is vitreous on crystal faces and pearly on cleavage surfaces. It is a relatively light mineral, with a density of about 3.1 g/cm³. ## Colors and Varieties Devilline occurs in a characteristic range of colors from greenish-blue, through blue-green, to almost pure green. The intensity and hue depend on the specific location and impurities. No named varieties are distinguished. ## History and Name The mineral was first described in 1864 by the French chemist and mineralogist Félix Pisani. The name "devilline" was given in honor of the French chemist Henri Étienne Sainte-Claire Deville (1818–1881), known for his work on aluminum and platinum. ## Uses Due to its rarity, small crystal size, and brittleness, devilline has no industrial applications. It is exclusively a mineral of scientific and collector's interest.

Properties

Mohs hardness
2.5
Luster
Vitreous, Pearly
Streak
Light green
Density
3.131
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The key diagnostic feature of devilline is its characteristic, radial aggregates of tiny, bladed crystals with an intense blue-green color. They often form rosette-like or small spherical shapes. The pearly luster on cleavage surfaces is also helpful in identification. ## Distinguishing from Similar Minerals Devilline can be confused with other secondary copper minerals. It is distinguished from brochantite and antlerite by its lighter, more blue hue and characteristic radial habit. It differs from aurichalcite by its darker color and lack of reaction with hydrochloric acid. Serpierite is very similar (and belongs to the same group), but often has a lighter, more bluish color; certain distinction requires advanced analysis. ## Crystal Forms Crystals are thin-tabular, pseudohexagonal, elongated, and bladed. They almost always occur in radial, fan-shaped, spherulitic, or rosette-like aggregates, as well as in druses and crusts with a velvety surface.

Geological environment

## Genesis Devilline is a secondary mineral, formed in the oxidation (weathering) zones of copper ore deposits, mainly sulfides such as chalcopyrite or bornite. It crystallizes from aqueous solutions rich in copper and sulfate ions, under conditions of low temperature and pressure. It often forms on the walls of old mine workings. ## Mineral Associations It most commonly co-occurs with other secondary copper minerals, such as brochantite, antlerite, malachite, azurite, linarite, and gypsum. Goethite and other iron oxides may also accompany it. ## Localities Significant specimens come from many places around the world. In Europe, it is known from mines in Špania Dolina (Slovakia), Cornwall (United Kingdom), Tuscany (Italy), and Lavrion (Greece). Beautiful specimens have also been found in mines in Arizona and Utah (USA).

Rarity

Rare

For collectors

## Quality Criteria The most prized devilline specimens are characterized by well-formed, distinct rosette-like or spherulitic aggregates with an intense, vibrant, blue-green color. High contrast with the host rock color is important. Large, undamaged coatings of devilline druses on matrix significantly increase the value of a specimen. Purity (absence of coatings of other minerals) is also desirable. ## Popular Localities The historical locality of Špania Dolina in Slovakia is considered classic and provides some of the best specimens. Specimens from mines in Cornwall, England, and some mines in Arizona, USA, are also highly valued.

Care and storage

## Cleaning Devilline specimens should be cleaned with the utmost care. Only gentle dusting with a soft brush to remove dirt is permissible. The use of water, especially warm water, is absolutely inadvisable, as the mineral is partially soluble in it. Ultrasonic cleaners should be avoided. ## What to Avoid Contact with all chemicals, including acids and detergents, should be avoided. The mineral is very sensitive to heat, which can lead to its dehydration and destruction. It should be protected from direct sunlight, which can cause fading. It is a very brittle mineral, sensitive to impacts and scratches. ## Storage Devilline specimens are best stored in closed, stable containers or display cases to protect them from dust, mechanical damage, and sudden changes in humidity. They should not be stored together with harder minerals.

External references

Sources

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