Wuyanzhiite

Chemical formula: Cu₁+₂S₂-

Wuyanzhiite is a rare copper(I) sulfide with a tetragonal structure, occurring as small, tabular crystals of a dark gray color.

## Characteristics Wuyanzhiite is a copper(I) sulfide and a polymorph of chalcocite and djurleite. It forms very small, tabular or platy crystals, reaching sizes up to 50 micrometers. Its color is dark gray, and on a fresh surface, it exhibits a metallic luster. It is an opaque mineral. Due to its extreme rarity and small crystal sizes, it is primarily of interest to specialized collectors and systematic mineralogists. ## Physical Properties The mineral is characterized by a hardness of approximately 3 on the Mohs scale and a density of 5.618 g/cm³. It has a metallic luster and a black streak. Its fracture is uneven. It is opaque. ## History and Name The mineral's name honors Wuyanzhi (born 1937), a Chinese mineralogist and crystallographer from the Institute of Geochemistry in Guangzhou, for his contributions to mineral research. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2017 (IMA2017-006).

Properties

Mohs hardness: 3-0
Luster: Metallic
Streak: black
Density: 5.618
Fracture: Irregular/Uneven
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Identification of wuyanzhiite is impossible without advanced analytical techniques, such as X-ray diffraction (XRD) and chemical analysis using an electron microprobe (EDS/WDS). Visually, it is indistinguishable from other copper sulfides with a similar appearance. ## Distinguishing from Similar Minerals It can be confused with chalcocite, djurleite, covellite, or bornite. Wuyanzhiite is distinguished from chalcocite (monoclinic) and djurleite (monoclinic) by its tetragonal crystallographic system. These differences can only be determined by laboratory methods. ## Crystal Forms It forms very small, thin, tabular crystals, often grouped into small aggregates. Crystals rarely exceed 50 micrometers in length and a few micrometers in thickness.

Geological environment

## Genesis It is a hydrothermal mineral, crystallizing under low-temperature conditions. It forms in copper-enriched zones within ore deposits. ## Mineral Associations At the type locality (Baifang mine), it coexists with chalcocite, djurleite, galena, sphalerite, pyrite, bornite, quartz, and calcite. ## Localities The only confirmed occurrence of wuyanzhiite in the world is its type locality: the Baifang mine, Changning County, Hengyang Prefecture, Hunan Province, China.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a wuyanzhiite specimen is determined by the presence of identifiable (even under a microscope) crystals on the rock matrix. Due to their microscopic size, any specimen with confirmed presence of this mineral is considered scientifically and collector-wise valuable. The richness of aggregates and association with other rare minerals enhances its attractiveness.

Care and storage

## Cleaning Due to the extreme rarity and microscopic size of its crystals, wuyanzhiite specimens should not be mechanically or chemically cleaned by collectors. Any attempts at cleaning may damage or remove the delicate crystals from the rock matrix. ## What to Avoid Avoid contact with chemicals, acids, and ultrasound. The mineral is susceptible to oxidation, which can alter its surface. It should be protected from moisture and sudden temperature changes. ## Storage Specimens should be stored under stable conditions, preferably in a closed, padded "micromount" box, to protect them from dust, mechanical damage, and humidity changes. Light exposure is not a major threat, but chemical stability is crucial.

External references

https://www.mindat.org/min-52595.html