Tvalchrelidzeite

Chemical formula: Hg₂+₃Sb₃+As₃-S₂-₃

Tvalchrelidzeite is a very rare mercury, antimony, and arsenic sulfide, forming small, metallic gray grains.

## Characteristics Tvalchrelidzeite is a sulfosalt mineral composed of mercury, antimony, and arsenic. It occurs as very fine, anhedral (irregularly shaped) grains, rarely exceeding 0.3 mm, disseminated in the host rock. Its appearance is inconspicuous – it forms steel-gray to black, metallic-lustered inclusions that can only be identified using advanced analytical techniques. ## Physical Properties This mineral is characterized by a metallic luster and a black streak. It is opaque. Due to the extremely small size of the crystals, most of its physical properties, such as hardness or density, have been estimated or calculated rather than directly measured on a larger fragment. ## Colors and Varieties No color varieties or commercial forms of this mineral are distinguished. Its only known form is a steel-gray to black mass. ## History and Name The mineral's name honors the Georgian geologist and mineralogist, Professor Alexander Tvalchrelidze (1881–1957), director of the Caucasian Institute of Mineral Resources. It was discovered and described in 1975 based on material from the Gomi deposit in Georgia.

Properties

Mohs hardness: 2.5
Luster: Metallic
Streak: Black
Density: 7.38
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying tvalchrelidzeite in field conditions or an amateur collection is practically impossible. It requires specialized analytical methods, such as X-ray microanalysis (EDS/WDS) in an electron microscope, to confirm its unique chemical composition (simultaneous presence of Hg, Sb, and As in sulfide form). ## Distinguishing from Similar Minerals It can be confused with many other fine-grained, gray sulfides and sulfosalts, such as cinnabar, stibnite, metacinnabar, or other mercury sulfosalts. It differs from them by its specific chemical composition, which is the only reliable diagnostic feature. ## Crystal Forms This mineral forms only small, anhedral (irregularly shaped) grains and aggregates. Well-formed crystals have not been observed.

Geological environment

## Genesis It is a hydrothermal mineral, forming under low-temperature conditions. It develops in zones of advanced argillization (alteration to clay minerals) in volcanic rocks, such as andesites and dacites, which have been subjected to hydrothermal solutions. ## Mineral Associations It most commonly co-occurs with other ore minerals, especially cinnabar, metacinnabar, pyrite, marcasite, laffittite, realgar, orpiment, and stibnite. It is also accompanied by rock-forming minerals and alteration products, such as quartz, chalcedony, kaolinite, and dickite. ## Localities The most important and primary occurrence (type locality) is the Gomi mercury deposit in the Racha-Lechkhumi and Kvemo Svaneti region of Georgia. This is the only confirmed and well-documented locality for this mineral worldwide.

Rarity

Extremely rare

For collectors

## Quality Criteria Tvalchrelidzeite specimens are not evaluated for aesthetic appeal, as the mineral is microscopic and does not form visually attractive shapes. The collectible and scientific value of a specimen lies solely in the confirmed presence of this extremely rare mineral, documented by appropriate analysis. The most valuable specimens are rock fragments with the highest possible concentration of tvalchrelidzeite grains, originating from the type locality.

Care and storage

## Cleaning Due to its microscopic size and occurrence as inclusions in rock, individual tvalchrelidzeite grains are not subject to cleaning. Host rock specimens should not be washed with strong chemicals. ## What to Avoid Avoid contact with acids and other aggressive chemicals that could react with sulfides. As a mercury- and arsenic-containing mineral, it requires careful handling to avoid inhaling dust or particles. ## Storage Specimens containing tvalchrelidzeite should be stored under stable conditions, in sealed containers or display cases, to limit potential mercury vapor release (though unlikely in this form) and protect against dust. The specimen should be clearly labeled due to its toxic chemical composition.

Sources

IMA Mineral List (CNMNC)