Hrabákite

Chemical formula: Ni₉PbSbS₈

Hrabákite is a very rare nickel, lead, and antimony sulfide, forming microscopic grains with a metallic luster.

## Characteristics Hrabákite is an extremely rare mineral from the hauchecornite group, a complex sulfide with the chemical composition Ni₉PbSbS₈. It occurs as very fine, anhedral (not exhibiting its own crystallographic forms) grains, reaching sizes up to 0.2 mm. It is usually intergrown with other ore minerals. Its color is gray with a brownish tint, and it has a metallic luster. ## Physical Properties This mineral is characterized by a hardness in the range of 5-6 on the Mohs scale. It is opaque and possesses a metallic luster. Its density, calculated based on the chemical formula and unit cell parameters, is 6.37 g/cm³. ## History and Name The mineral is named in honor of Milan Hrabák (1936-1985), a Czech amateur mineralogist from Příbram, who first found this mineral. Hrabákite was described and approved as a new mineral species by the International Mineralogical Association (IMA) in 2021 (IMA2021-031).

Properties

Mohs hardness
5-6
Luster
Metallic
Density
6.37
Transparency
Opaque
Crystal system
Tetragonal

Diagnostic features

## Identification Identification of hrabákite is impossible without advanced analytical techniques. It requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm the presence of nickel, lead, antimony, and sulfur in appropriate proportions. Optically, in reflected light, it is difficult to distinguish from other co-occurring sulfides. ## Distinguishing from Similar Minerals It can be confused with other minerals from the hauchecornite group (e.g., hauchecornite, tučekite) and other gray sulfides, such as ullmannite or gersdorffite. Definitive differentiation requires chemical composition analysis and crystallographic data (X-ray diffraction). ## Crystal Forms This mineral forms exclusively microscopic, irregular grains intergrown with other minerals. No well-formed crystals have been observed.

Geological environment

## Genesis Hrabákite forms as a result of hydrothermal processes. In its type locality, it was found in calcite veins cutting Proterozoic sedimentary rocks. ## Mineral Associations This mineral co-occurs with other ore minerals. At the discovery site, it was found in association with ullmannite, gersdorffite, tučekite, hauchecornite, calcite, cassiterite, chalcopyrite, pyrite, sphalerite, galena, and quartz. ## Localities The only confirmed locality for hrabákite worldwide is its type locality: Uranium Mine No. 9 (Shaft No. 9) in Háje, Příbram region, Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral of purely scientific value, it is not subject to standard quality assessment criteria applied to macroscopic specimens. Its collector's value lies in possessing an analytically confirmed rock fragment (a "micromount") from the type locality, containing this mineral. Every specimen with confirmed hrabákite is extremely valuable from a scientific point of view.

Care and storage

## Cleaning Due to its extreme rarity and microscopic nature, mechanical cleaning is neither recommended nor possible. Specimens should be analyzed in the state in which they were found. ## What to Avoid Contact with chemicals, especially acids, which can react with sulfides, should be avoided. Ultrasound and sudden temperature changes should also be avoided. As an ore mineral, it may be susceptible to oxidation in humid environments. ## Storage Specimens containing hrabákite should be stored under stable, dry conditions, preferably in sealed "micromount" containers, to protect them from dust, moisture, and mechanical damage.

External references

Sources

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