Carlinite

Chemical formula: Tl₁+₂S₂-

Carlinite is a rare thallium sulfide, forming tiny, metallic grains with a characteristic black color and streak.

## Characteristics Carlinite is a very rare mineral from the sulfide group, composed of thallium and sulfur. It occurs as very fine, anhedral (not exhibiting its own crystalline form) grains, dispersed in the host rock, most often in carbonized organic matter or in association with other ore minerals. Its grains rarely exceed 0.5 mm in size. It is black and opaque in appearance, with a metallic luster. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 1-1.5. It has a relatively high density, approximately 8.1 g/cm³, which is a result of the high content of the heavy element, thallium. Carlinite's luster is metallic, and its streak is black. ## Colors and Varieties Carlinite is an idiochromatic mineral, meaning its chemical composition determines its color. It is invariably black. No color varieties or commercial varieties are distinguished. ## History and Name Carlinite was discovered in 1975 in the Carlin gold mine in Eureka County, Nevada (USA). Its name comes directly from the discovery locality. It was described by Arthur S. Radtke and Frank W. Dickson. Due to its chemical composition (high content of toxic thallium), it is a mineral of scientific interest. ## Uses Due to its extreme rarity and occurrence as microscopic grains, carlinite has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals.

Properties

Mohs hardness: 1-1.5
Luster: Metallic
Streak: Black
Density: 8.1
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identifying carlinite under amateur conditions is practically impossible due to the microscopic size of its grains and its resemblance to other black sulfides. Recognition requires advanced laboratory methods, such as EDS/WDS analysis (electron microprobe) to confirm its chemical composition (presence of thallium and sulfur exclusively). Its extreme softness and black streak are auxiliary features but insufficient for certain identification. ## Distinguishing from Similar Minerals Carlinite can be confused with many other black, metallic minerals with which it co-occurs, such as lorandite, getchellite, pyrite, or marcasite. Distinguishing it "by eye" or with simple tests is impossible. Chemical analysis is required. ## Crystal Forms Carlinite forms exclusively anhedral, irregular grains, often with rounded or irregular outlines. No well-formed crystals have been observed.

Geological environment

## Genesis Carlinite is a low-temperature hydrothermal mineral. It forms by deposition from thallium- and sulfur-rich solutions at temperatures below 150°C. It typically forms in "Carlin-type" gold deposits, where it is disseminated in sedimentary rocks (siltstones, limestones) rich in organic matter and carbonates. ## Mineral Associations This mineral co-occurs with other thallium sulfides and sulfosalts, such as lorandite, getchellite, christite, as well as realgar, orpiment, pyrite, marcasite, quartz, calcite, and barite. It is also often accompanied by gold, albeit in the form of microscopic inclusions. ## Localities The most important and typical occurrence of carlinite is in the gold deposits of northern Nevada, USA, particularly the Carlin mine (type locality) in Eureka County. It is also known from several other localities worldwide, including the Lanmuchang mercury deposit in Guizhou Province, China, and the Vorontsovskoye gold deposit in the Urals, Russia.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a carlinite specimen is primarily assessed based on the richness and size of visible grains in the host rock. Since this mineral is microscopic, specimens where clusters of black grains can be observed under magnification are considered valuable. Contrast with a light host rock (e.g., quartz) enhances visual appeal. Co-occurrence with other rare thallium minerals also significantly increases collectible value. ## Popular Localities By far the most prized and classic specimens come from the Carlin gold mine in Nevada, USA. Material from this locality is considered reference for the species.

Care and storage

## Cleaning Specimens containing carlinite should generally not be wet cleaned. Due to its occurrence as fine, embedded grains, cleaning is usually not necessary. If needed, compressed air can be used to remove dust. ## What to Avoid Carlinite is a mineral containing highly toxic thallium. Inhaling dust and direct skin contact must be strictly avoided. Hands should be thoroughly washed after any contact with a specimen. It must not be heated or exposed to acids, which can release toxic compounds. Keep away from children and pets. ## Storage Carlinite specimens should be stored in tightly sealed, clearly labeled containers or display boxes, with a label warning of toxicity. It is best to keep it separate from other minerals to avoid accidental contamination of the collection.

Sources

IMA Mineral List (CNMNC)