Polhemusite

Chemical formula: (Zn₂+,Hg₂+)S₂-

Polhemusite is a very rare zinc and mercury sulfide, forming microscopic, metallic grains in sedimentary rocks.

## Characteristics Polhemusite is an extremely rare mineral from the sulfide group, chemically classified as a zinc and mercury sulfide. It occurs as very fine, irregular grains, usually not exceeding 0.1 mm in size. Observed under a microscope in reflected light, it has a grayish-white color with a slight creamy tint and exhibits a metallic luster. Due to its microscopic size, its macroscopic features are unknown. ## Physical Properties Due to the microscopic size of the grains, most physical properties, such as hardness, density, or fracture, have not been precisely measured. The luster is metallic. The mineral is opaque. ## History and Name Polhemusite was discovered in samples from the Potosi Formation in southeastern Missouri, USA. It was described in 1978 by H. H. Haddock, P. C. D. Grice, and S. A. Williams. The name honors Clyde P. Polhemus (1903–1975), a mining geologist who first observed this mineral. ## Uses Polhemusite has no commercial or industrial applications. Its significance is purely scientific and as a collector's item, as a unique member of the sulfide group.

Properties

Mohs hardness: 4.5
Color: Black
Luster: Metallic
Density: 0
Cleavage: Rare
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Identification of polhemusite is possible only through advanced laboratory techniques, such as electron microprobe analysis (EDS/WDS) to confirm its chemical composition (presence of zinc, mercury, and sulfur) and reflected light microscopy. In reflected light, it is grayish-white and exhibits weak anisotropy. ## Distinguishing from Similar Minerals Under the microscope, it can be confused with other fine-grained, metallic sulfides, such as sphalerite, galena, or cinnabar. Differentiation requires chemical analysis. Sphalerite does not contain mercury, and cinnabar does not contain zinc in significant quantities. ## Crystal Forms Polhemusite forms only anhedral (irregular), rounded grains and aggregates of microscopic size, dispersed in the host rock. No well-formed crystals have been observed.

Geological environment

## Genesis Polhemusite forms under low-temperature hydrothermal conditions. In its type locality (Missouri, USA), it occurs in dolomites, where it crystallized in rock voids and fractures from solutions rich in zinc and mercury. ## Mineral Associations This mineral co-occurs with other sulfides, primarily sphalerite, as well as galena, marcasite, and pyrite. Associated minerals also include dolomite and quartz. ## Localities The only confirmed and well-documented occurrence of polhemusite in the world is its type locality in Washington County, Missouri, USA, within the so-called "Viburnum Trend," an important lead and zinc mining region.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a polhemusite specimen depends solely on the abundance and concentration of microscopic grains in the host rock and on the confirmation of their identity by analysis. Macroscopic specimens are not visually attractive. The most valuable samples are from the type locality, with the largest amount of analytically confirmed mineral, often in association with well-formed crystals of sphalerite or galena.

Care and storage

## Cleaning Specimens containing polhemusite, due to the microscopic nature of the mineral, usually do not require and should not be cleaned. Any attempts at mechanical or chemical cleaning may destroy the fine grains embedded in the host rock. ## What to Avoid Avoid contact with chemicals, acids, and ultrasound. Do not subject the specimen to rapid temperature changes. As a mercury-containing mineral, it requires careful handling; avoid inhaling dust and wash hands after contact. ## Storage Specimens should be stored under stable conditions, in a closed display box, to protect them from dust and mechanical damage. It is recommended to clearly label the sample due to its mercury content.

External references

https://www.mindat.org/min-3253.html