Raguinite

Chemical formula: Tl<sup>1+</sup>Fe<sup>3+</sup>S<sup>2-</sup><sub>2</sub>

Raguinite is a rare thallium iron sulfide, forming tiny, prismatic crystals with a metallic luster.

## Characteristics Raguinite is a rare mineral from the sulfide group, composed of thallium, iron, and sulfur. It occurs as very small, elongated, prismatic crystals, rarely exceeding 1 mm in length. It usually forms granular aggregates or occurs as inclusions in other minerals. Its appearance is inconspicuous, and identification requires specialized equipment. ## Physical Properties Raguinite crystals exhibit a strong metallic luster. The mineral is opaque and has a black streak. Its hardness on the Mohs scale is approximately 2, making it a soft mineral. The density is high, around 7.35 g/cm³. ## Colors and Varieties Raguinite ranges in color from brownish-red to black. No color or commercial varieties are distinguished. ## History and Name The mineral was discovered in the Allchar deposit in North Macedonia and described in 1969. Its name honors the French mineralogist and geologist Eugène Raguin (1900-2001), a professor at the École Nationale Supérieure des Mines de Paris. ## Uses Due to its extreme rarity and small crystal size, raguinite has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals.

Properties

Mohs hardness
2
Luster
Metallic
Streak
Black
Density
7.35
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Amateur identification of raguinite is practically impossible. It requires advanced analytical methods, such as chemical composition analysis (EDS) and X-ray diffraction (XRD). Helpful characteristics may include: high density, metallic luster, brownish-red color, and co-occurrence with other thallium minerals. ## Distinguishing from Similar Minerals Raguinite can be confused with other small, dark sulfides, such as pyrite, chalcopyrite, or lorandite. Differentiation is based on chemical analysis – the presence of thallium and iron in a specific ratio is key. Unlike pyrite, raguinite is significantly softer. ## Crystal Forms It forms very small, acicular or prismatic crystals, elongated along one of the crystallographic axes. Crystals often show striations on their faces. It also occurs as granular aggregates and irregular inclusions.

Geological environment

## Genesis Raguinite is a low-temperature hydrothermal mineral. It forms in ore deposits where solutions rich in thallium, arsenic, antimony, and sulfur are present. Its crystallization occurs in the final stages of mineral-forming processes. ## Mineral Associations It most commonly co-occurs with other thallium minerals, such as lorandite and vrbaite, as well as with realgar, orpiment, marcasite, and pyrite. These minerals form a characteristic mineral assemblage at its occurrence site. ## Localities The most important and type locality for raguinite is the Allchar (Alsar) deposit in North Macedonia. This is the only locality from which well-formed and studied specimens of this mineral originate. It has also been reported in the Lanmuchang mercury deposit in Guizhou Province, China.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a raguinite specimen primarily depends on the possibility of its identification and observation. Microscopic specimens showing clearly formed, individual crystals or rich aggregates are most valued. Their association with other rare thallium minerals, such as lorandite or orpiment, is also important, increasing the scientific and collector's value of the specimen. Size and color are of secondary importance due to the microscopic nature of the mineral. ## Popular Localities The only source of collectible specimens is the historic Allchar deposit in North Macedonia. Specimens from this locality are highly sought after by collectors specializing in rare and "systematic" minerals.

Care and storage

## Cleaning Raguinite specimens are generally not cleaned due to their size, fragility, and embedding in the host rock. Any attempt at mechanical or chemical cleaning risks destroying the mineral. If absolutely necessary, compressed air can be used to remove loose dust particles. ## What to Avoid Avoid contact with chemicals, acids, and detergents. The mineral is soft and susceptible to scratches. Protect it from moisture and sudden temperature changes. ## Storage Raguinite specimens should be stored under stable conditions, preferably in sealed "micromount" boxes that protect them from dust, mechanical damage, and moisture. Avoid exposure to direct sunlight.

Sources

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