Erzwiesite

Chemical formula: Ag₁+₈Pb₂+₁₂Bi₃+₁₆S₂-₄₀

Erzwiesite is a rare lead-silver-bismuth sulfosalt with a metallic luster, occurring as small, intergrown grains.

## Characteristics Erzwiesite is a complex sulfosalt of lead, silver, and bismuth. It occurs as very small, anhedral (irregular) grains, typically up to 200 micrometers in size. These grains are most often intergrown with other minerals, mainly galena. Due to the microscopic size of the specimens, visual features observable with the naked eye are practically impossible to detect. In polished sections under a microscope, it is white with a slight creamy tint and exhibits weak pleochroism. ## Physical Properties Due to its microscopic nature, most physical properties, such as hardness, density, cleavage, or fracture, have not been precisely determined. The mineral is characterized by a metallic luster and is opaque. ## Colors and Varieties The mineral has a steel-gray to black color. In reflected light, it is white with a creamy tint. No varieties are distinguished. ## History and Name Erzwiesite was first described in 2014 by a team of mineralogists led by Dan Top. Its name comes from the historic Erzwies mine in Gasteinertal, Hohe Tauern (Austria), where the mineral was discovered. This is the type locality for this mineral. It was approved by the International Mineralogical Association (IMA) under number 2013-124.

Properties

Luster: Metallic
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of erzwiesite is possible only through advanced laboratory techniques, such as electron microprobe analysis (EMPA) in reflected light on polished sections. Its microscopic size and occurrence as intergrowths make recognition impossible under field conditions or based on macroscopic features. ## Distinguishing from Similar Minerals Under the microscope, it can be confused with other silver, lead, and bismuth sulfosalts, such as members of the lillianite group. Differentiation requires precise chemical analysis. From galena, in which it often occurs, it differs in reflected light by a slightly different color and optical properties. ## Crystal Forms Erzwiesite forms exclusively anhedral, irregular grains, usually intergrown with other minerals. No well-formed crystals have been observed.

Geological environment

## Genesis Erzwiesite forms as a result of hydrothermal processes. At its type locality (Erzwies mine), it is associated with Alpine gold and silver veins that cut through gneisses and amphibolite schists. It formed during a late stage of mineralization, crystallizing from solutions rich in lead, bismuth, silver, and sulfur. ## Mineral Associations This mineral occurs in close association with galena, in which it forms intergrowths. It is also accompanied by other sulfosalts, such as vikingite, eskimoite, as well as chalcopyrite, sphalerite, pyrite, arsenopyrite, native gold, and quartz. ## Localities The only confirmed and thoroughly described occurrence of erzwiesite in the world is its type locality – the historic Erzwies mine, located in the Gastein Valley, in the Hohe Tauern mountain range, in the state of Salzburg, Austria.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, erzwiesite is not traded as individual collector specimens. Its value is purely scientific and related to the richness of the mineral association on a sample from the type locality. The attractiveness of a specimen with erzwiesite depends on the quality and aesthetics of the associated minerals, and erzwiesite itself is merely a valuable, analytically confirmed addition for specialized systematic or regional collections (so-called "micromounts").

Care and storage

## Cleaning Due to its microscopic size and occurrence as intergrowths within other minerals, isolated cleaning of erzwiesite is not practical. Specimens containing this mineral should be treated according to the requirements of the main mineral (matrix), most often galena. ## What to Avoid Aggressive chemicals, acids, and ultrasonic cleaners should be avoided, as they could damage both the mineral itself and the surrounding rock matrix. ## Storage Specimens should be stored under stable conditions, away from moisture and contaminants, preferably in sealed collector boxes, to prevent the oxidation of sulfides.

Sources

IMA Mineral List (CNMNC)