Thalliomelane
Chemical formula: Tl¹⁺Mn⁴⁺₇.₅Cu²⁺₀.₅O₁₆
Thalliomelane is a rare manganese and thallium oxide, distinguished by its black color and occurrence in the form of small, radial aggregates.
Properties
- Luster
- Metallic
- Streak
- Black
- Density
- 5.285
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Tetragonal
Diagnostic features
## Identification Macroscopically, thalliomelane is practically indistinguishable from other black, fibrous manganese oxides, such as cryptomelane, hollandite, or manjiroite. Its characteristic feature is radial aggregates of small, acicular crystals. Definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS) to confirm the presence of thallium, copper, and manganese. ## Differentiation from Similar Minerals It is distinguished from other minerals of the cryptomelane group (hollandite, cryptomelane, manjiroite) by the presence of thallium as the dominant cation in a specific structural position. Visually, they are identical. ## Crystal Forms This mineral forms very fine, acicular or fibrous crystals up to 0.1 mm long. These crystals aggregate into radial, spherulitic forms or create felt-like clusters.
Geological environment
## Genesis Thalliomelane is a hydrothermal mineral. It forms in the oxidation zones of polymetallic deposits, where manganese and thallium concentrate under low-temperature conditions. It occurs in calcite veins cutting volcanic rocks. ## Mineral Associations In the type locality (Siberian Platform), thalliomelane co-occurs with calcite, quartz, native copper, tenorite, malachite, azurite, and other manganese oxides of the cryptomelane group. ## Localities The only confirmed and described locality for thalliomelane is its discovery site – an unspecified location on the Siberian Platform in Russia.
Rarity
Extremely rare
For collectors
## Quality Criteria Thalliomelane is a mineral of purely scientific and systematic significance. It does not form specimens attractive to the typical collector. Its value lies in its rarity and being a representative of an unusual chemical composition. The best specimens are those with well-formed, visible under magnification, radial aggregates on a contrasting background (e.g., on calcite) and originate from the type locality, with analytically confirmed identity.
Care and storage
## Cleaning Thalliomelane specimens, due to their delicate, fibrous structure, should be cleaned with utmost care. It is safest to use compressed air to remove dust. Any contact with water or brushes can irrevocably damage the fine aggregates. ## What to Avoid All chemicals, including acids and detergents, should be avoided. The mineral is susceptible to mechanical damage, so it should be protected from impacts, scratches, and vibrations. It should not be subjected to ultrasonic cleaning. ## Storage It is recommended to store specimens in closed, padded collector's boxes to protect them from dust and physical damage. Display should be in stable conditions, away from high-traffic areas.