Tischendorfite

Chemical formula: Pd₈Hg₃Se₉

Tischendorfite is a very rare palladium and mercury selenide, forming small, metallic grains of a tin-white color.

## Characteristics Tischendorfite is an extremely rare mineral from the selenide group, characterized by a complex chemical composition containing palladium, mercury, and selenium. It occurs as very small, anhedral (irregularly shaped) grains, usually not exceeding 200 micrometers in size. It is observed in polished sections under a microscope, where it reveals its tin-white color and metallic luster. Due to its extreme rarity and microscopic size, it does not form macroscopic specimens or crystals visible to the naked eye. ## Physical Properties This mineral is characterized by a strong metallic luster. It is opaque. Its Mohs hardness is estimated at 2.5, and its VHN10 microhardness is 84 kg/mm². The density has been calculated as 9.05 g/cm³. ## History and Name The name tischendorfite comes from Gerhard Tischendorf (1927-2007), a German geologist and mineralogist who made significant contributions to the study of selenium deposits in the Harz region of Germany. The mineral was approved by the IMA in 2001, and its description was published in 2002. The type locality (locus typicus) is the former Eskaborner uranium mine, located in the Tilkerode area in the Harz Mountains.

Properties

Mohs hardness: 2.5
Luster: Metallic
Streak: Black
Density: 9.05
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of tischendorfite is possible only through advanced laboratory techniques. Under a reflected light ore microscope, it exhibits a tin-white color, weak pleochroism (from white to creamy white), and distinct anisotropy with bluish to brownish color effects. Final confirmation requires chemical composition analysis (e.g., using an electron microprobe) and X-ray diffraction data. ## Distinguishing from Similar Minerals It can be confused with other microscopic platinum-group metal selenides, such as chrisstanleyite, oosterboschite, or clausthalite, with which it often co-occurs. Differentiation is based on precise measurements of reflectivity and hardness, as well as chemical analysis. ## Crystal Forms This mineral occurs as anhedral, irregular grains intergrown with other minerals. No well-formed crystals have been observed.

Geological environment

## Genesis It is a hydrothermal mineral. It forms under low-temperature conditions in calcite-dolomite veins, where it precipitates along with other selenides. ## Mineral Associations It most commonly co-occurs with clausthalite, chrisstanleyite, oosterboschite, umangite, klockmannite, berzelianite, tiemannite, eucairite, uraninite, hematite, and goethite. These minerals form complex, microscopic intergrowths. ## Localities The only confirmed locality for tischendorfite in the world is its type locality – the Tilkerode deposit in the Harz Mountains, Saxony-Anhalt, Germany. This is a historic mining area known for its unique selenium mineralogy.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its microscopic nature, tischendorfite is not a collector's item in the traditional sense. Polished sections or rock fragments from the type locality, in which the presence of the mineral has been analytically confirmed, have scientific and collector value. Samples rich in intergrowths with other rare selenides, with thoroughly documented analysis, are most highly prized.

Care and storage

## Cleaning Due to its microscopic nature within the host rock, specimens do not require and are not suitable for cleaning in the traditional sense. Any attempts at mechanical or chemical cleaning would destroy the mineral. ## What to Avoid All chemicals, ultrasonics, and any mechanical intervention should be avoided. Specimens should be protected from dust and contaminants. ## Storage Tischendorfite specimens, typically in the form of polished sections or rock fragments, should be stored under stable conditions in specialized boxes or containers that protect against physical damage and dust. They do not require humidity control or protection from light.

Sources

IMA Mineral List (CNMNC)