Tučekite

Chemical formula: Ni₉Sb₂S₈

Tučekite is a rare, metallic nickel, antimony, and sulfur mineral, forming microscopic, silvery-white grains in serpentinite rocks.

## Characteristics Tučekite is a nickel antimony sulfide, occurring as very small, irregular grains or lamellar aggregates, rarely exceeding 0.5 mm. Observed under a microscope in reflected light, it has a creamy-white color with a slight pinkish tint and exhibits weak anisotropy. It is an opaque mineral with a metallic luster. ## Physical Properties Due to the microscopic size of the grains, most physical properties are difficult to determine precisely. The Vickers hardness (VHN) is 215-240 kg/mm², which approximately corresponds to a value of about 4 on the Mohs scale. The density calculated based on the chemical formula and unit cell parameters is 7.15 g/cm³. ## History and Name The mineral was discovered in serpentinites in the locality of Kanowna, Western Australia. Described in 1978 by J. Just and C. E. Feather, it was named in honor of Dr. Karel Tuček (1904-1990), a Czech mineralogist and former curator of the mineralogical collections at the National Museum in Prague, for his contributions to mineralogy. ## Applications Tučekite has no commercial or industrial significance. Its occurrence is solely of scientific and collector's value, being of interest to specialized collectors of rare minerals.

Properties

Mohs hardness: 4
Luster: Metallic
Density: 7.15
Cleavage: None
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of tučekite is only possible using advanced laboratory methods, such as reflected light ore microscopy and chemical analysis with an electron microprobe (EDS/WDS). Visually, it is impossible to distinguish from other metallic minerals without appropriate magnification and analytical equipment. In reflected light, it is characterized by a creamy-white color and weak anisotropy. ## Distinguishing from Similar Minerals It can be confused with other nickel sulfides, such as pentlandite, heazlewoodite, or millerite, as well as nickel antimonides, e.g., breithauptite. Definitive distinction requires chemical composition analysis, which will show the simultaneous presence of nickel, antimony, and sulfur in characteristic proportions. ## Crystal Forms Tučekite does not form well-developed crystals. It occurs exclusively as anhedral (irregular) grains and lamellar aggregates intergrown with other minerals.

Geological environment

## Genesis Tučekite is a hydrothermal mineral, associated with the serpentinization processes of ultramafic rocks (peridotites, dunites). It forms at low temperatures as a result of metasomatic alterations of primary nickel sulfide and arsenide minerals under the influence of antimony-rich solutions. ## Mineral Associations This mineral coexists with other nickel sulfides and antimonides. In the type locality (Kanowna, Australia), it was found in association with heazlewoodite, pentlandite, millerite, polydymite, as well as rare minerals such as orcelite and breithauptite. It occurs as inclusions in serpentine and magnetite. ## Localities Tučekite is an extremely rare mineral, identified in only a few locations worldwide. Besides the type locality in Kanowna, Western Australia, its presence has been confirmed in the ultramafic rock complex in Ransko, Czech Republic, and in the nickel-copper deposit in Koryak-Kamchatka in the Russian Far East.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, tučekite is not evaluated according to typical criteria such as size or crystal form. The collector's value of a specimen lies in the analytically confirmed presence of the mineral and the richness of the mineral association on the sample. The most desirable specimens are from the type locality (Kanowna), containing the largest possible number of tučekite grains visible under the microscope, in association with other rare nickel minerals. ## Popular Localities The only source of specimens of significance to specialized collectors is its type locality - Kanowna in Western Australia. Specimens from other, few localities are practically unavailable on the collector's market.

Care and storage

## Cleaning Specimens containing tučekite, due to the microscopic nature of the mineral and its occurrence as inclusions within the host rock, generally do not require and should not undergo cleaning. Any attempts at mechanical or chemical cleaning may damage the delicate mineral grains or the surrounding rock. If necessary, dust can be removed with a gentle stream of compressed air. ## What to Avoid Avoid contact with acids and other aggressive chemicals that may react with sulfides. Do not subject the specimen to ultrasound or sudden temperature changes. Store away from humid environments to prevent potential oxidation. ## Storage Tučekite specimens are best stored under stable conditions, in a closed "micromount" box, to protect them from dust, mechanical damage, and moisture. The label should include the exact locality, as the value of the specimen is closely tied to it.

Sources

IMA Mineral List (CNMNC)