Barrotite

Chemical formula: Cu₂+₉Al(HSiO₄)₂(S₆+O₄)(HAs₅+O₄)₀.₅(OH)₁₂·₈H₂O

An extremely rare mineral from the group of copper silicates, sulfates, and arsenates, forming characteristic blue, hexagonal crystals.

## Characteristics Barrotyite is a very rare, complex hydrated copper and aluminum sulfate, silicate, and arsenate. It occurs as small, thin, hexagonal crystals with a platy habit. These crystals often arrange themselves into visually attractive groups resembling rosettes or fans. It is a secondary mineral, meaning it forms as a result of the alteration of other minerals. It is the trigonal dimorph of monoclinic gabyite, to which it is closely related. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 2. It is characterized by a vitreous luster and is translucent. Its density, calculated from the chemical formula and unit cell parameters, is approximately 3.21 g/cm³. It exhibits perfect cleavage in one plane, parallel to the base of the hexagonal crystals. ## Colors and Varieties Barrotyite has a characteristic, intensely blue color. No color varieties or commercial varieties are known. ## History and Name The mineral is named in honor of Cèsar-Marie-Joseph Barrot (1800-1885), a French professor of physics and chemistry from Avignon. It was officially recognized by the International Mineralogical Association (IMA) in 2011. The type locality, or first place of discovery, is the Cap Garonne mine in Le Pradet, Var department, France. ## Applications Due to its extreme rarity and occurrence as microscopic crystals, barrotyite has no industrial applications. It is of purely scientific importance and is a highly valued object in advanced mineral collections.

Properties

Mohs hardness: 2
Luster: Vitreous
Streak: Pale blue
Density: 3.21
Cleavage: Perfect on {0001}
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification The key diagnostic feature of barrotyite is its unique crystal form – thin, hexagonal plates, often in the form of rosettes. The intensely blue color, vitreous luster, and occurrence exclusively in one location worldwide (Cap Garonne mine) are also characteristic. Identification is confirmed by its co-occurrence with other rare, secondary copper minerals. ## Differentiation from Similar Minerals Barrotyite can be confused with its monoclinic dimorph, gabyite, which has an identical chemical composition but different crystal symmetry. Differentiation requires advanced research methods (e.g., X-ray diffraction). From other blue copper minerals, such as cyanotrichite, it is distinguished by its crystal habit (cyanotrichite forms needles and fibers), and from linarite or azurite – by different physical and chemical properties. ## Crystal Forms Barrotyite crystallizes as thin, hexagonal plates. These crystals rarely occur individually, most often forming radial aggregates, fans, and rosettes, growing on the host rock.

Geological environment

## Genesis Barrotyite is a secondary mineral, forming in the oxidation zone of polymetallic deposits. Its formation is post-mining, meaning it crystallizes as a result of processes occurring in old, abandoned mine workings. It forms from the reaction of waters percolating through rocks (sandstones) with primary ore minerals, mainly tennantite. ## Mineral Associations This mineral occurs in association with other rare, secondary copper and arsenic minerals. It most often co-occurs with its dimorph gabyite, as well as with olivenite, tennantite, covellite, chalcocite, cuprite, devilline, brochantite, posnjakite, langite, cyanotrichite, and serpierite. ## Localities The only confirmed locality of barrotyite in the world is the Cap Garonne mine, located in Le Pradet, in the Provence-Alpes-Côte d'Azur region of France. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The collector's value of barrotyite specimens depends on several factors. Samples with well-formed, sharp hexagonal crystals forming aesthetic rosettes are most highly prized. The intensity and purity of the blue color are also important. The size of the crystal aggregates and the contrast with the rock matrix are of great significance. Specimens with rich associations of other rare minerals from Cap Garonne are particularly sought after. ## Popular Localities All collector's specimens of barrotyite come from a single location – the Cap Garonne mine in France. This locality is known worldwide for the occurrence of unique, secondary arsenic minerals and is considered one of the most important localities for micromineralogy.

Care and storage

## Cleaning Barrotyite specimens are extremely delicate and should be handled with the utmost care. For dust removal, it is best to use compressed air from a safe distance. If necessary, a very brief rinse in distilled water is permissible, followed by immediate drying with an air stream. Any friction should be avoided. ## What to Avoid The mineral is very soft and brittle, making it susceptible to mechanical damage. Contact with all chemicals, including acids and detergents, should be avoided. Ultrasonic cleaners must not be used. As a hydrated mineral, it may be sensitive to high temperatures, which can lead to its dehydration and destruction. ## Storage Collector's specimens of barrotyite, usually micromounts, should be stored in specialized boxes that protect them from dust, shocks, and direct contact. Stable humidity and temperature conditions should be maintained, away from direct sunlight.

Sources

IMA Mineral List (CNMNC)