Holubite

Chemical formula: Ag₁+₃Pb₂+₆(Sb₃+₈Bi₃+₃)S₂-₂₄

Holubite is a rare sulfosalt mineral of lead, silver, antimony, and bismuth, forming tiny, metallic-lustered crystals.

## Characteristics Holubite is a complex sulfosalt mineral belonging to the lillianite group. It forms very small, acicular or bladed crystals, rarely exceeding 1 mm in length, which occur as inclusions in galena or as aggregates in quartz druses. It has a steel-gray to black color and a metallic luster. ## Physical Properties Due to the small size of the crystals, most physical properties have not been precisely determined. Hardness is estimated at approximately 3-4 on the Mohs scale. Density, calculated based on the chemical formula and unit cell parameters, is 6.43 g/cm³. The mineral is opaque and exhibits a metallic luster. ## Colors and Varieties Holubite occurs in a uniform, steel-gray to black color. No varieties have been distinguished. ## History and Name The mineral was approved by the IMA in 2017 (IMA2017-050). Its name honors the Czech mineralogist and collector, Milan Holub (born 1971), who is a specialist in ore mineralogy and was the first to find this mineral. It was described by a team of Czech scientists led by Jiří Sejkora. ## Uses Holubite has no industrial application. It is of purely scientific and collector's interest as a very rare mineral.

Properties

Mohs hardness: 3-4
Luster: Metallic
Streak: Black
Density: 6.43
Cleavage: Imperfect on {100}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of holubite is impossible without advanced analytical methods, such as X-ray microanalysis (EDS/WDS) and X-ray diffraction (XRD). Visually, it is indistinguishable from many other fine sulfosalts, such as lillianite, gustavite, or terrywallaceite. It occurs as tiny, acicular inclusions in galena or in quartz druses. ## Distinguishing from similar minerals Practically all similar sulfosalts (e.g., from the lillianite group) require chemical analysis for certain distinction. Holubite is characterized by a specific ratio of Ag, Pb, Sb, and Bi in its structure. ## Crystal Forms Holubite forms prismatic, acicular, or bladed crystals, elongated along the b-axis. Crystals are very small, typically up to 1 mm in length and tens of micrometers thick. They often occur as irregular aggregates or inclusions.

Geological environment

## Genesis Holubite forms under hydrothermal conditions, in ore veins containing polymetallic mineralization. In the type locality (Kutná Hora), it occurs in quartz-carbonate veins cutting gneisses. ## Mineral Associations This mineral coexists with galena (often as inclusions), quartz, sphalerite, pyrite, chalcopyrite, arsenopyrite, tetrahedrite, lillianite, gustavite, terrywallaceite, pyroxenes (diopside-hedenbergite), and carbonates (siderite, ankerite). ## Localities The only confirmed and described locality in the world from which holubite originates (type locality) is the historical mining region of Kutná Hora in the Czech Republic, specifically the Roveň shaft dump.

Rarity

Very rare

For collectors

## Quality Criteria As a "micromount" type mineral, the collector's value of holubite primarily depends on the confirmation of its identity through analysis. The most valuable specimens are those where well-formed, even microscopic, crystals are visible in a quartz druse, rather than just as inclusions in galena. The richness of association with other rare sulfosalts also increases the specimen's value. ## Popular Localities The only source of specimens is the type locality - Kutná Hora in the Czech Republic. The material comes from historical dumps, and its acquisition is very limited.

Care and storage

## Cleaning Specimens containing holubite should generally not be cleaned mechanically or chemically due to their delicacy and rarity. The tiny crystals are extremely fragile. If dust removal is necessary, compressed air from a safe distance or a very soft brush can be used. ## What to avoid Avoid contact with chemicals, acids, and detergents, which can damage both holubite and associated minerals (e.g., galena). It should not be subjected to ultrasonic cleaning. Protect it from high temperatures and humidity. ## Storage Specimens should be stored under stable conditions, in closed "micromount" boxes, to protect them from dust, mechanical damage, and sudden temperature changes. Due to the small size of the crystals, they are easily lost or damaged.

Sources

IMA Mineral List (CNMNC)