Iltisite

Chemical formula: Hg₂+Ag₁+S₂-Cl

Iltisite is a very rare silver-mercury sulfide-chloride mineral, forming microscopic, hexagonal crystals with a metallic luster.

## Characteristics Iltisite is a sulfide mineral whose chemical composition includes silver, mercury, sulfur, and chlorine. It occurs as extremely small, hexagonal, tabular crystals, rarely exceeding 50 micrometers in diameter and a few micrometers in thickness. These crystals often form rosette-like or irregular aggregates. Due to its microscopic size, it is a mineral primarily accessible to specialized collectors and scientific institutions. ## Physical Properties Iltisite crystals exhibit a metallic luster. They are opaque and have a black color with a black streak. Hardness and density have not been precisely measured due to the small size of the samples; however, the density calculated based on the formula and unit cell parameters is 7.86 g/cm³. ## History and Name The mineral was named after Antoine Iltis (born 1936), a French chemist and mineral collector from Mulhouse, France, who provided the first samples for study. It was approved by the International Mineralogical Association (IMA) in 1995. It was described by S. Ghose, R. C. Rouse, and J. D. Grice based on material from the Silberbrünnl mine in Gengenbach, Black Forest, Germany.

Properties

Luster: Metallic
Streak: Black
Density: 7.86
Cleavage: Perfect on {0001}
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of iltisite is only possible using advanced analytical methods, such as scanning electron microscopy (SEM) with EDS analysis or X-ray diffraction (XRD). Visual identification in the field or even under a standard microscope is practically impossible due to its microscopic size and resemblance to other black minerals. ## Distinguishing from similar minerals It can be confused with other fine-grained, black sulfides or oxides that may co-occur in similar environments. Certain differentiation requires confirmation of its unique chemical composition, simultaneously containing Ag, Hg, S, and Cl. ## Crystal forms Iltisite forms very small, thin, hexagonal crystals with a tabular habit. These crystals often arrange themselves into rosette-like or irregular aggregates on the surface of the host rock.

Geological environment

## Genesis Iltisite is a secondary mineral, forming in the oxidation zones of silver and mercury ore deposits. It forms as a result of low-temperature hydrothermal processes. At its type locality (Gengenbach), it occurs in barite-fluorite veins cutting gneisses. ## Mineral associations This mineral co-occurs with other secondary silver and mercury minerals. The most common associated minerals include: native mercury, calomel, eglestonite, terlinguaite, cordierite, quartz, barite, and fluorite. ## Localities Confirmed occurrences of iltisite are extremely rare. Apart from the type locality in the Silberbrünnl mine in Gengenbach (Black Forest, Germany), it has only been identified in a few other places worldwide, including the McDermitt mine in Humboldt County, Nevada, USA.

Rarity

Extremely rare

For collectors

## Quality criteria Due to the microscopic nature of the mineral, the main criterion for collector value is the abundance and quality of crystals visible under a microscope. Specimens with clearly formed, hexagonal crystals or dense aggregates that contrast well with the matrix are most prized. Association with other rare secondary minerals is also important. ## Popular localities The only source of specimens of collector significance is the type locality – the Silberbrünnl mine in Gengenbach, Germany. Specimens from other localities are rarities primarily of scientific importance.

Care and storage

## Cleaning Iltisite specimens, due to their microscopic size and delicacy, should generally not be cleaned mechanically or chemically. Any attempts at cleaning may destroy or dislodge the tiny crystals from the matrix. It is safest to leave the specimen in its untouched state. ## What to avoid Avoid contact with any chemicals, vibrations, and temperature changes. As a mercury-bearing mineral, it should be handled with caution. Avoid inhaling dust and wash hands after contact with the specimen. ## Storage Specimens should be stored in stable conditions, in closed, padded "micromount" boxes to protect them from physical damage, dust, and contamination. Storage away from heat sources and direct sunlight is recommended.

Sources

IMA Mineral List (CNMNC)