Tilkerodeite
Chemical formula: Pd₂HgSe₃
Tilkerodeite is a very rare palladium and mercury selenide, forming microscopic, metallic grains in association with other selenides.
Properties
- Mohs hardness
- 3
- Color
- Black or gray
- Luster
- Metallic
- Streak
- Black
- Density
- 9.67
- Cleavage
- {001}
- Transparency
- Opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Identification of tilkerodeite is possible only with advanced laboratory techniques, such as ore microscopy in reflected light and chemical analysis using an electron microprobe (EDS/WDS). In reflected light, it exhibits weak pleochroism and anisotropy. It is unrecognizable to the naked eye. ## Distinguishing from Similar Minerals It can be confused with other microscopic selenides that occur with it, such as clausthalite, tiemannite, umangite, or klockmannite. Definitive differentiation requires chemical analysis, as all these minerals form very similar, metallic-lustered grains. Tilkerodeite is distinguished by its unique combination of palladium, mercury, and selenium. ## Crystal Forms Tilkerodeite occurs exclusively as anhedral (irregular) grains and aggregates, ranging in size from a few to about 100 micrometers. It often forms intergrowths with other selenides. It has not been observed in the form of well-developed crystals.
Geological environment
## Genesis Tilkerodeite forms as a result of low-temperature hydrothermal processes. Its formation is associated with selenide mineralization in calcite-ankerite veins cutting through clay shales. It is a secondary mineral, crystallizing in a late stage of deposit evolution. ## Mineral Associations This mineral occurs in close association with other, much more common selenides. It most frequently co-occurs with clausthalite, tiemannite, umangite, klockmannite, eucairite, berzelianite, and eskebornite. Associated minerals also include hematite and calcite. ## Localities The only confirmed locality for tilkerodeite in the world is its type locality – the area of the former mines in Tilkerode (Abberode), in the Harz Mountains, Saxony-Anhalt, Germany. This is a historical and well-known locality for many rare selenides.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a specimen with tilkerodeite is determined not by the microscopic mineral itself, but by the richness and quality of the co-occurring, more visible selenides (e.g., clausthalite, umangite). The most highly valued samples are those where the presence of tilkerodeite has been confirmed by analysis, and the specimen itself is rich in other, well-formed minerals from this paragenesis. The size and quantity of tilkerodeite grains, although only assessable in the laboratory, also increase the scientific and collector value of the specimen. ## Popular Localities All known specimens come from a single location worldwide: the historical mining area of Tilkerode in the Harz Mountains, Germany. Specimens from this locality, especially those with confirmed presence of tilkerodeite, are extremely sought after by specialized collectors of rare minerals.
Care and storage
## Cleaning Specimens containing tilkerodeite should generally not be cleaned. The mineral is microscopic, brittle, and embedded in a matrix. Any attempt at mechanical or chemical cleaning may irreversibly damage or remove the tiny mineral grains. ## What to Avoid Avoid contact with chemicals, ultrasonics, and all forms of abrasive cleaning. Samples should be protected from dust and contaminants that might later require cleaning. ## Storage Specimens should be stored under stable conditions, in sealed "micromount" containers, to protect them from mechanical damage and dust. Exposure to strong light or humidity changes is not recommended, although their impact on this particular mineral has not been fully investigated.