Carboirite

Chemical formula: Fe<sup>2+</sup>Al<sub>2</sub>GeO<sub>5</sub>(OH)<sub>2</sub>

Carboirite is an extremely rare iron and aluminum germanate, known only from one locality in the world.

## Characteristics Carboirite is a germanate analogue of chloritoid, belonging to a group of rare minerals. It forms small, prismatic crystals, rarely exceeding 1 mm in length. Most often, they occur as radial or subparallel aggregates, forming small rosettes or intergrown clusters in quartz. Its appearance is subtle, and specimens are primarily of scientific interest and for specialized collectors. ## Physical Properties Carboirite crystals exhibit a hardness of approximately 6 on the Mohs scale. They have a vitreous luster and are translucent. The calculated density for this mineral is 3.85 g/cm³, which is a relatively high value, resulting from the presence of iron and germanium in its structure. ## Colors and Varieties This mineral is characterized by a pale, pink, or grayish-pink coloration. No color varieties or commercial forms are known. ## History and Name Carboirite was first described in 1978 by François Fontan, François Permingeat, and Roland Pierrot. Its name comes from the Pic de Carboire peak, located near the mineral's discovery site in the Eastern Pyrenees, France. ## Applications Due to its extreme rarity and occurrence as microscopic crystals, carboirite has no industrial applications. It serves solely as an object of scientific research and a valuable specimen in advanced systematic collections.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
White
Density
3.85
Cleavage
Perfect on {110}
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification The key diagnostic feature of carboirite is its locality – this mineral is known only from one place in the world. Preliminary identification is possible due to its pale pink color, occurrence as small, radial aggregates in quartz veins, and co-occurrence with cassiterite. Final confirmation of identity requires advanced chemical analyses (e.g., EDS) to detect germanium. ## Distinguishing from Similar Minerals Carboirite is visually almost identical to its silicate counterpart, chloritoid. Differentiating these two minerals without chemical analysis is impossible. It can also be confused with other pink silicate minerals, but its unique geological environment and paragenesis with cassiterite are strong indicators. ## Crystal Forms Carboirite forms elongated, prismatic crystals of small size (usually less than 1 mm). These crystals often intergrow into rosette-like or radial aggregates, as well as subparallel clusters.

Geological environment

## Genesis This mineral forms under low-temperature hydrothermal conditions. Its occurrence is limited to quartz veins cutting through Paleozoic schists. Germanium, a key component of carboirite, was likely released and concentrated during hydrothermal processes from the surrounding metamorphic rocks. ## Mineral Associations Carboirite occurs in close association with quartz, which is the main component of the veins. Other minerals found in its environment include cassiterite and chlorite. ## Localities The only confirmed and described locality of carboirite in the world is the area of Costabonne peak (Pic de Costabonne) in the Pyrénées-Orientales department, Occitanie region, France.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of carboirite specimens, being a microscopic mineral, is primarily assessed based on the abundance and development of crystals on the matrix. Samples with clearly formed, sharp crystals forming aesthetic aggregates are most valued. The intensity of the pink color and the presence of associated minerals, such as cassiterite, which enhance the scientific and visual value of the specimen, are also important. ## Popular Localities The only source of collectible specimens is the type locality – the area around Costabonne peak in the French Pyrenees. Specimens from this location are extremely difficult to acquire and appear on the market very rarely.

Care and storage

## Cleaning Carboirite specimens should be cleaned very carefully, preferably with a soft brush dry to remove dust. If necessary, distilled water can be used. Ultrasonic cleaners should be avoided, as they could damage the delicate crystals due to their perfect cleavage. ## What to Avoid The mineral should be protected from contact with strong acids. Prolonged exposure to moisture may not be advisable due to its iron content. There is no detailed data on its sensitivity to light or temperature, but standard precautions, such as avoiding extreme conditions, are recommended. ## Storage The safest way to store carboirite is to place it in a sealed "micromount" box, which protects delicate crystals from mechanical damage, dust, and moisture.

Sources

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