Kupčíkite
Chemical formula: Cu<sub>3.4</sub>Fe<sub>0.6</sub>Bi<sub>5</sub>S<sub>10</sub>
Kupčíkite is a rare copper, iron, and bismuth sulfide, forming acicular crystals with a metallic luster.
Properties
- Mohs hardness
- 3.5
- Luster
- Metallic
- Streak
- Black
- Density
- 6.45
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Kupčíkite is identified by its characteristic form – thin, acicular or bladed crystals of a steel-gray color and metallic luster. It often forms tangled or radial aggregates. Its co-occurrence with other bismuth sulfides and sulfosalts is also key. ## Distinguishing from Similar Minerals It can be confused with other acicular bismuth sulfosalts, such as bismuthinite, aikinite, or emplectite. Final differentiation from these minerals often requires advanced analytical methods, such as chemical composition analysis (EDS) or X-ray diffraction (XRD), as they are visually very similar. ## Crystal Forms Crystals are strongly elongated, acicular, bladed, often with visible longitudinal striations. They usually occur as tangled aggregates, radial clusters, or chaotically arranged needles grown on other minerals, mainly quartz.
Geological environment
## Genesis It is a hydrothermal mineral, forming in ore veins. It crystallizes at medium to low temperatures in paragenesis with other bismuth, copper, and lead sulfides and sulfosalts. ## Mineral Associations It most commonly co-occurs with bismuthinite, emplectite, hodrushite, chalcopyrite, pyrite, quartz, and native bismuth. Depending on the locality, other rare sulfosalts may also accompany it. ## Localities The most important and classic localities for this mineral are: - **Slovakia**: Ľubietová (Libethen), particularly the Podlipa deposit, where it was discovered (type locality). - **Czech Republic**: Horní Slavkov (Schlaggenwald) in the Slavkov Forest. - **Japan**: Ikuno Mine in Hyōgo Prefecture on Honshu Island.
Rarity
Very rare
For collectors
## Quality Criteria Specimens with well-formed, sharp, and undamaged acicular crystals are most valued by collectors. Rich, radial aggregates or dense clusters of needles on a contrasting matrix, most often white quartz, are highly prized. The size of the crystals is also important – specimens with needles exceeding a few millimeters are rare. The purity of the specimen and the absence of mechanical damage are crucial. ## Popular Localities Specimens from the type locality, Ľubietová in Slovakia, have the greatest historical and scientific value. Specimens from Horní Slavkov in the Czech Republic and the Ikuno Mine in Japan also appear on the collector's market and are equally sought after by specialists.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. The use of water or any chemical agents that could react with the sulfides and cause oxidation or damage is not recommended. ## What to Avoid Avoid contact with water, acids, detergents, and other chemicals. The mineral is sensitive to moisture, which can lead to its slow oxidation and the formation of tarnish. It should be protected from high temperatures and sudden temperature changes. ## Storage It is recommended to store specimens in a dry place, preferably in tightly sealed "membrane boxes" or in display cases away from moisture. Limiting air access will slow down oxidation processes and help preserve the mineral's natural luster.