Capgaronnite

Chemical formula: AgHgClS

Capgaronnite is a rare silver mercury chloride sulfide, forming tiny, prismatic crystals with a metallic luster.

## Characteristics Capgaronnite is a very rare mineral from the sulfide group. It occurs as very small, prismatic or acicular crystals, rarely exceeding 1 mm in length. It also forms radial aggregates or granular masses. Its crystals are typically elongated and striated along the vertical axis. Due to its chemical composition, containing mercury and silver, it is a toxic mineral. ## Physical Properties This mineral is characterized by a metallic luster and is opaque. Its Mohs hardness is 2, meaning it is very soft and easily scratched. The density is high, which is typical for minerals containing mercury and silver. ## Colors and Varieties Capgaronnite is gray to black, often with a metallic luster. No color varieties or commercial varieties are known. ## History and Name The mineral's name comes from its discovery locality - the Cap-Garonne mine in France. It was first described in 1992 by a team of mineralogists: W.H. Paar, Y. Moëlo, W.G. Mumme, and T.T. Chen. It was approved by the International Mineralogical Association (IMA) in 1991. ## Applications Capgaronnite has no industrial applications. Its significance is purely scientific and as a collector's item, being a very rare and chemically unique mineral.

Properties

Mohs hardness
2
Luster
Metallic
Streak
Black
Density
6.19
Cleavage
Good on {101}
Fracture
Uneven
Transparency
Opaque
Crystal system
Tetragonal

Diagnostic features

## Identification Identifying capgaronnite under amateur conditions is practically impossible. Identification requires advanced analytical methods, such as chemical analysis (EDS/WDS) to confirm the presence of silver, mercury, sulfur, and chlorine, and X-ray diffraction (XRD) to determine the crystal structure. Visually, it is simply a small, dark gray or black, metallic mineral. ## Distinguishing from similar minerals It can be confused with many other small, dark sulfides or sulfosalts, such as acanthite, galena, or other rare mercury minerals. Definitive distinction is only possible based on chemical and structural analysis. ## Crystal forms Capgaronnite forms very small, prismatic or acicular crystals, often elongated and striated. It also occurs as radial aggregates or grains.

Geological environment

## Genesis Capgaronnite is a secondary mineral. It forms in the oxidation zones (gossans) of polymetallic ore deposits, as a result of the weathering of primary sulfides, especially tennantite. Its formation is associated with the presence of chlorine-rich waters. ## Mineral associations This mineral co-occurs with other secondary minerals, such as olivenite, tennantite, covellite, chalcocite, djurleite, tennantite-tenorite, and also with quartz. ## Localities The most important and type locality for capgaronnite is the Cap-Garonne mine in Le Pradet, Var, France. It is a very rare mineral, and its occurrence has been confirmed only in this single locality worldwide.

Rarity

Extremely rare

For collectors

## Quality criteria As an extremely rare "micromineral," any analytically confirmed capgaronnite specimen is valuable to specialized collectors. Specimens with well-formed, even microscopic, crystals that are clearly visible on the rock matrix are most highly prized. Contrast with other colorful secondary minerals (e.g., blue covellite) also enhances the visual appeal and value of the specimen. ## Popular localities The only known and confirmed locality from which all collector specimens originate is the Cap-Garonne mine in France. This is a classic locality for many rare secondary minerals.

Care and storage

## Cleaning Due to its extreme rarity and fragility, capgaronnite specimens should only be cleaned by specialists. They generally do not require cleaning. If absolutely necessary, compressed air can be used to remove dust. Avoid contact with water and chemicals. ## What to avoid The mineral is very soft (hardness 2), so any physical contact that could scratch or damage it should be avoided. As a mercury-containing mineral, it is toxic - avoid inhaling dust and direct skin contact. Wash hands after any contact. Do not heat, as this may release toxic mercury vapors. ## Storage Capgaronnite specimens should be stored in stable, sealed containers (e.g., "perky box" type) to protect them from mechanical damage and dust. They should be kept in a dry place, away from heat sources and direct sunlight. Due to its toxicity, the container should be clearly labeled, and the specimen stored out of reach of children and pets.

External references

Sources

Read more