Brodtkorbite

Chemical formula: Cu¹⁺₂Hg²⁺Se²⁻₂

Brodtkorbite is a rare copper-mercury selenide, forming tiny, metallic-lustered grains of a dark gray color.

## Characteristics Brodtkorbite is a very rare mineral from the sulfide group, belonging to the selenides. It occurs as very fine, anhedral (irregularly shaped) grains, usually not exceeding 100 micrometers in size. Its typical specimens have a dark gray color and a metallic luster. Due to the small size of the crystals, it is a mineral primarily observable under a microscope. ## Physical Properties This mineral is characterized by a Mohs hardness ranging from 2.5 to 3, classifying it as a soft mineral. It is opaque and has a metallic luster. Its fracture is uneven. ## Colors and Varieties Brodtkorbite occurs in a uniform, dark gray color. No color or commercial varieties are known. ## History and Name The mineral's name honors Milka K. de Brodtkorb, an Argentine mineralogist and professor of geology at the University of Buenos Aires, in recognition of her contributions to the study of Argentine mineralogy. It was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 1999, and its discovery took place in the Tumiñico mine in Argentina.

Properties

Mohs hardness: 2.5-3
Luster: Metallic
Streak: Dark grey
Density: 0
Fracture: Irregular/Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying brodtkorbite is extremely difficult and impossible to perform in the field without specialized equipment. Recognition requires advanced laboratory techniques, such as chemical composition analysis using an electron microprobe (EDS/WDS) and X-ray diffraction (XRD) analysis. Its key feature is its unique chemical composition – a copper-mercury selenide. ## Distinguishing from Similar Minerals Under a microscope, it can be confused with other fine, gray selenides or sulfides with a metallic luster, such as umangite, berzelianite, or eucairite. Definitive differentiation is only possible based on chemical analysis. ## Crystal Forms Brodtkorbite forms only very fine, anhedral (irregularly shaped) grains, most often with a diameter of less than 0.1 mm. No well-formed crystals are observed.

Geological environment

## Genesis Brodtkorbite forms as a result of low-temperature hydrothermal processes. Its formation is associated with the presence of solutions rich in selenium, copper, and mercury. It occurs in calcite veins cutting volcanic rocks, such as dacites. ## Mineral Associations This mineral occurs in association with other selenides. In its type locality (Tumiñico mine), it was found in association with clausthalite, umangite, berzelianite, eucairite, klockmannite, tyrrellite, as well as with hematite and calcite. ## Localities The only confirmed and thoroughly described occurrence of brodtkorbite in the world is its type locality – the Tumiñico mine in the Sierra de Cacho mountain range, La Rioja Province, Argentina.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its extreme rarity and microscopic size, brodtkorbite is not evaluated according to typical collector criteria, such as size or crystal form. The collector value of a specimen lies in the very fact of the confirmed presence of this mineral. The most valuable samples are from the type locality, with the richest concentration of brodtkorbite grains, well-documented, and with analytically confirmed identification. ## Popular Localities The only source of specimens is the Tumiñico mine in Argentina. This mineral is practically unavailable on the open collector market and is found mainly in institutional and research collections.

Care and storage

## Cleaning Due to its extreme rarity and small grain size, brodtkorbite specimens are not subjected to standard cleaning. They are usually permanently embedded in the host rock and studied in their unaltered form. ## What to Avoid Any attempts at mechanical or chemical cleaning that could destroy the microscopic mineral grains should be avoided. As a mercury-containing selenide, it is sensitive to acids and high temperatures. Contact with chemicals should be avoided. ## Storage Specimens should be stored under stable conditions, in specialized collector boxes, away from moisture, dust, and direct light. It is best to keep them in the original host rock in which they were found.

External references

https://www.mindat.org/min-7090.html