Edenharterite

Chemical formula: Tl₁+Pb₂+As₃+₃S₂-₆

Edenharterite is a rare lead, thallium, and arsenic sulfosalt, forming acicular crystals with a metallic luster.

## Characteristics Edenharterite is a rare mineral from the sulfosalt group, composed of lead, thallium, and arsenic. It occurs as very small, acicular or bladed crystals, rarely exceeding 1 mm in length. These crystals often form tangled aggregates or radial clusters. The mineral is characterized by its black color and metallic luster, giving it an appearance similar to other sulfosalts. ## Physical Properties Edenharterite is a relatively soft mineral, with a Mohs hardness of approximately 2.5. It is opaque and possesses a metallic luster. Its density is significant, around 5.6 g/cm³, which is typical for lead-bearing minerals. ## Colors and Varieties This mineral is uniform in color and occurs exclusively in black. No color varieties or commercial forms are distinguished. ## History and Name Edenharterite was discovered in the Lengenbach quarry in the Binn Valley (Binntal), Switzerland, a locality known for its unique sulfosalts. It was described in 1991 by J. Pasi and E.J. Graeser. The mineral is named in honor of Andreas Edenharter (born 1944), an Austrian chemical crystallographer from the University of Göttingen, for his contributions to the study of synthetic sulfosalts. ## Uses Due to its extreme rarity and microscopic crystal size, edenharterite has no industrial applications. It is solely an object of scientific interest and a collector's item for specialized systematic mineral and micromount collectors.

Properties

Mohs hardness: 2.5
Luster: Metallic
Streak: Red-brown
Density: 5.59
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identifying edenharterite is extremely difficult without advanced analytical methods. Visually, it is a black, metallic mineral forming small, acicular crystals. Key to identification is the locality of occurrence (Lengenbach quarry) and its association with other rare sulfosalts. Definitive identification requires chemical analysis (EDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Edenharterite is practically impossible to distinguish with the naked eye from many other sulfosalts found in the same locality, such as hutchinsonite, wallisite, imhofite, or sartorite. All form similar, dark, metallic crystals. Differences can only be determined based on chemical composition and crystal structure analysis. ## Crystal Forms Edenharterite forms elongated, acicular or bladed crystals, often exhibiting striations along the elongation axis. These crystals usually occur as tangled, woolly aggregates or small, radial clusters growing on other minerals, primarily dolomite.

Geological environment

## Genesis Edenharterite forms as a result of hydrothermal processes in metamorphic deposits. In its type locality, the Lengenbach quarry, it crystallizes in fissures and small cavities within dolomitic marbles (the so-called "Bündnerschiefer Dolomite"). It is believed that the source of arsenic, thallium, lead, and sulfur were hydrothermal solutions associated with Alpine metamorphic processes. ## Mineral Associations This mineral co-occurs with a rich assemblage of other rare arsenic, lead, and thallium sulfosalts. The most common associated minerals include: realgar, orpiment, hutchinsonite, hatchite, wallisite, sartorite, baumhauerite, rathite, as well as dolomite, on which it most often crystallizes. ## Localities The only confirmed and described locality for edenharterite in the world is the Lengenbach quarry in the Binn Valley (Binntal), Valais canton, Switzerland. This is the type locality for this mineral.

Rarity

Very rare

For collectors

## Quality Criteria The quality of edenharterite specimens is primarily assessed based on the richness and development of crystals within the aggregate. Most valued are specimens with clearly visible, though still microscopic, acicular crystals forming dense clusters. Contrast with a light substrate (usually white dolomite) also enhances visual appeal. The size of individual crystals is rarely the main criterion, as all are very small. ## Popular Localities The only source of edenharterite specimens is its type locality - the Lengenbach quarry in Switzerland. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Edenharterite specimens are extremely delicate and small. Mechanical cleaning is not recommended. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Avoid ultrasonic cleaners, steam cleaners, acids, and detergents. The mineral is sensitive to chemicals and can be damaged. Protect it from high temperatures and sudden temperature changes. ## Storage Edenharterite specimens, typically as micromounts, should be stored in stable conditions, in sealed boxes protecting them from dust and mechanical damage. Due to the presence of toxic elements (thallium, lead, arsenic), it should be kept out of reach of children and pets, and hands should always be washed after handling the mineral.

Sources

IMA Mineral List (CNMNC)