Tillmannsite

Chemical formula: (HgAg<sub>3</sub>)<sup>3+</sup>V<sup>5+</sup>O<sub>4</sub>

Tillmannsite is a rare silver and mercury vanadate, forming small, yellow crystals with a metallic luster.

## Characteristics Tillmannsite is a vanadate mineral characterized by a unique chemical composition containing mercury and silver. It occurs as very small, tabular or bladed crystals, rarely exceeding 0.2 mm in length. These crystals often form irregular aggregates or rosettes. Due to its small size, its features are difficult to observe without a microscope. ## Physical Properties Tillmannsite crystals exhibit a metallic to submetallic luster. Hardness and density have not been precisely determined due to the small size of samples and the rarity of the mineral. It is opaque. ## Colors and Varieties This mineral has a characteristic bright yellow color. The streak is also bright yellow. No color or commercial varieties are known. ## History and Name Tillmannsite was first described in 2003 by Werner Kraus, Joel Brugger, Mark A. Cooper, Frank C. Hawthorne, S. J. Kolitsch, and A. R. Lang. The mineral is named in honor of Heinz-Günter Tillmann (born 1940), a German mineral collector from Düsseldorf, who specialized in minerals from the Tsumeb mine and provided the sample for study. ## Uses Due to its extreme rarity and microscopic size, tillmannsite has no industrial applications. It is of purely scientific interest and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness
2.5
Luster
Metallic
Streak
Light yellow
Density
7.68
Cleavage
Perfect on {0001}
Fracture
Micaceous
Transparency
Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Identifying tillmannsite in the field is practically impossible. Identification requires advanced laboratory techniques, such as chemical analysis (EDS) and X-ray diffraction (XRD). In a collection, under a microscope, it can be identified based on its bright yellow color, metallic luster, and characteristic crystal form, provided it occurs on a known matrix from a typical locality. ## Distinguishing from Similar Minerals It can be confused with other rare, secondary yellow minerals, such as schneiderhöhnite or other vanadates. Definitive differentiation is possible only through chemical analysis, which will reveal the unique combination of silver, mercury, and vanadium. ## Crystal Forms Tillmannsite forms very small, thin, tabular crystals, often with a hexagonal or pseudohexagonal outline. These crystals group into irregular aggregates, rosettes, or occur as single, scattered flakes on the host rock.

Geological environment

## Genesis Tillmannsite is a secondary mineral, forming in the oxidation zones of polymetallic deposits rich in vanadium, silver, and mercury. It forms under arid, desert climatic conditions, as a result of the weathering of primary sulfide ores. ## Mineral Associations This mineral occurs in association with other rare secondary minerals. At its type locality (Tsumeb mine), it was found in association with tenorite, quartz, calcite, hematite, anglesite, schneiderhöhnite, otjisumeite, and owamboite. ## Localities The only confirmed occurrence of tillmannsite in the world is its type locality – the Tsumeb mine in the Otjikoto Region, Namibia. This is one of the most famous mineralogical sites globally, known for its extraordinary diversity and quality of minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a tillmannsite specimen is primarily assessed based on the abundance and visibility of crystals on the matrix. The most desirable specimens are those with well-formed, though still microscopic, crystals or dense aggregates of intense yellow color. Contrast with associated minerals, such as dark tenorite, also enhances aesthetic value. ## Popular Localities The only source of specimens is the Tsumeb mine in Namibia. All samples available on the collector's market come from this single, historic locality.

Care and storage

## Cleaning Due to the microscopic size of the crystals and their fragility, mechanical cleaning is not recommended. If necessary, compressed air (from a safe distance) can be used to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Avoid ultrasonics, steam cleaners, acids, and solvents. The mineral is potentially sensitive to changes in temperature and humidity. As a mercury-containing mineral, it requires careful handling to avoid inhaling dust. ## Storage Tillmannsite specimens should be stored under stable conditions, in sealed "micromount" containers, to protect them from dust, mechanical damage, and contamination. Keep them away from direct sunlight and heat sources.

Sources

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