Belendorffite

Chemical formula: Cu<sub>₇</sub>Hg<sub>₆</sub>

Belendorffite is a very rare natural copper-mercury amalgam, forming metallic, silvery-white grains and flakes.

## Characteristics Belendorffite is a natural alloy (amalgam) of copper and mercury. It occurs as small, irregular grains, flakes, or coatings on other minerals, usually not exceeding 1 mm in size. Its surface is typically silvery-white, often with a metallic luster, although it may tarnish or develop a patina over time. ## Physical Properties This mineral is opaque and exhibits a strong, metallic luster. It is malleable and ductile, meaning it can be deformed without breaking. Its hardness is low, and its density is very high due to the significant content of mercury and copper. ## Colors and Varieties Belendorffite has a characteristic silvery-white color, which may be slightly pinkish on a fresh surface. Over time, its surface may darken. No varieties of this mineral are distinguished. ## History and Name The mineral was discovered in the Backofen mine in Landsberg, near Obermoschel in Rhineland-Palatinate (Germany). It was described and approved by the IMA in 1992. Its name honors Klaus Belendorff (born 1953), a German mineral collector who found the first samples of this mineral. ## Uses Due to its extreme rarity and small size of occurrences, belendorffite has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors.

Properties

Mohs hardness: 2
Luster: Metallic
Streak: Silver-white
Density: 12.55
Cleavage: None
Fracture: Hackly
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Key diagnostic features include its silvery-white color, strong metallic luster, high density, and co-occurrence with other mercury minerals in their typical localities. Its malleability and ductility are also characteristic. However, identification requires advanced analytical methods, such as chemical composition analysis (EDS). ## Distinguishing from Similar Minerals Belendorffite can be confused with native mercury, which is liquid at room temperature, whereas belendorffite is a solid. It can also be confused with other amalgams, such as moschellandsbergite (silver amalgam), from which it is distinguished by the absence of silver in its composition and often a pinkish tint. Definitive differentiation requires specialized studies. ## Crystal Forms Belendorffite does not form well-developed crystals. It occurs exclusively as anhedral (irregular) grains, granular aggregates, flakes, and as coatings on other minerals.

Geological environment

## Genesis Belendorffite is a low-temperature hydrothermal mineral. It forms in the oxidation zones of mercury-bearing ore deposits, as a result of direct precipitation from solutions rich in copper and mercury. ## Mineral Associations This mineral co-occurs with native mercury, cinnabar, calomel, moschellandsbergite, as well as copper minerals such as native copper and cuprite. ## Localities The most important and classic locality (type locality) is the Backofen mine in Landsberg, near Obermoschel in Germany. Its occurrence has also been confirmed in mercury mines in the Almadén region of Spain and in several locations in the USA, including San Benito County, California.

Rarity

Very rare

For collectors

## Quality Criteria The collecting appeal of belendorffite is determined by the richness and size of its occurrences on the rock matrix. Specimens with clearly visible, abundant aggregates of silvery grains, contrasting with the substrate, are most valued. Good documentation of the specimen's provenance is also important, especially if it comes from the type locality. ## Popular Localities Specimens from the type locality – the Backofen mine in Germany – are by far the most sought after by collectors. Material from this location is considered classic for this mineral species.

Care and storage

## Cleaning Belendorffite specimens should generally not be cleaned. Any mechanical or chemical intervention risks damaging or destroying delicate occurrences. Contact with water and chemical agents should be avoided. ## What to Avoid The mineral is sensitive to elevated temperatures, which can cause the release of toxic mercury vapors. Heating must be absolutely avoided. It should be protected from acids and other chemicals. Due to its mercury content, direct skin contact should be avoided, and it should be stored away from food. ## Storage It is recommended to store specimens in sealed, airtight containers (e.g., "perky box" type) to limit potential mercury evaporation and protect the mineral from mechanical damage and dust. It should be kept at a stable room temperature, away from heat sources and direct sunlight.

Sources

IMA Mineral List (CNMNC)