Wittite
Chemical formula: Pb²⁺₈Bi³⁺₁₀(S²⁻,Se²⁻)₂₃
Wittite is a rare lead bismuth sulfide with selenium admixture, forming lamellae and aggregates with a metallic luster.
Properties
- Mohs hardness
- 2-2.5
- Luster
- Metallic
- Streak
- Black
- Density
- 0
- Cleavage
- One good cleavage. Cleabage surfaces show striations at 57° to 57.5°.
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Wittite can be identified by its lead-gray color, metallic luster, very low hardness, and characteristic form of thin, flexible lamellae. The streak of the mineral is black. Good cleavage in one direction, with visible striations on cleavage surfaces, is also an important diagnostic feature. ## Distinguishing from similar minerals Wittite is sometimes confused with other lead and bismuth sulfosalts, such as galenobismutite or lillianite, as well as with graphite or molybdenite due to similar appearance and low hardness. It differs from graphite and molybdenite by its higher density and lack of a characteristic "greasy" feel. Certain differentiation from other sulfosalts usually requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal forms This mineral rarely forms well-developed crystals. It is most often found in the form of thin, lamellar or flaky aggregates. Fibrous and radial aggregates are also observed.
Geological environment
## Genesis Wittite is a hydrothermal mineral. It forms in ore veins, usually in paragenesis with other bismuth and lead sulfides and sulfosalts. Its typical formation environment is polymetallic deposits. ## Mineral associations This mineral co-occurs with minerals such as bismuthinite, galena, chalcopyrite, quartz, calcite, as well as other, rarer sulfosalts. ## Localities The most important and historical occurrence of wittite is the Falun mine in the Dalarna region of Sweden, which is its type locality. Beyond Sweden, its presence has been noted in several other places worldwide, but these occurrences are of scientific significance only.
Rarity
Very rare
For collectors
## Quality criteria The quality of a wittite specimen is assessed based on the abundance and development of its aggregates. The most desirable specimens are those with clearly visible, undamaged lamellae or radial aggregates, contrasting with the surrounding rock (matrix). Due to the rarity of the mineral, every well-documented specimen has collector's value. ## Popular localities The only source of specimens of collector's significance remains the historical type locality – the Falun mine in Sweden. Specimens from this location, especially those from old collections, are the most valued.
Care and storage
## Cleaning Wittite specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to its low hardness and lamellar structure, it is extremely susceptible to mechanical damage. Water and any chemical agents should be avoided. ## What to avoid This mineral is sensitive to scratches, impacts, and abrasion. It should be protected from contact with harder minerals. Chemicals, including acids and bases, can damage it. Prolonged exposure to moisture can lead to its slow oxidation. ## Storage Wittite should be stored in a separate, padded display box to avoid contact with other minerals and prevent physical damage. It is not sensitive to light, but should be kept in a dry place.