Treasurite
Chemical formula: Ag<sub>7</sub>Pb<sub>6</sub>Bi<sub>15</sub>S<sub>30</sub>
Treasuryite is a rare silver, lead, and bismuth sulfosalt, forming acicular crystals with a metallic luster.
Properties
- Mohs hardness
- 3.5
- Luster
- Metallic
- Streak
- Black
- Density
- 6.41
- Cleavage
- Imperfect on {010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Treasuryite can be identified by its characteristic acicular or hair-like crystal form, steel-gray color, and metallic luster. Its high density is also an important clue. It occurs in paragenesis with other bismuth and lead sulfosalts. ## Distinguishing from Similar Minerals It can be confused with other acicular sulfosalts, such as jamesonite, boulangerite, or aikinite. Final differentiation from these minerals often requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS), due to subtle differences in chemical composition and physical properties. ## Crystal Forms It forms elongated, acicular crystals, often with a square or rectangular cross-section. These crystals can occur as single needles or form dense, tangled aggregates resembling felt.
Geological environment
## Genesis Treasuryite is a hydrothermal mineral. It forms in medium- to high-temperature ore veins rich in bismuth, lead, and silver. Its crystallization is associated with the activity of hydrothermal solutions in metamorphic and igneous rocks. ## Mineral Associations It often co-occurs with other sulfosalts and sulfides. Its typical associated minerals include aikinite, bismuthinite, galena, pyrite, quartz, as well as other rare sulfosalts from the lillianite group, such as gustavite or vikingite. ## Localities The most important and type locality for treasuryite is the Treasury Mine in the Geneva-Democrat area, Clear Creek County, Colorado, USA. It is also known from several other localities worldwide, including the Julcani Mine in Peru and some occurrences in Japan and Slovakia, where it is found in similar geological environments.
Rarity
Very rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, distinct acicular crystals, forming rich, dense aggregates on a rock matrix, most often on quartz. The contrast between the dark, metallic needles of treasuryite and the light quartz background is particularly desired. The size of the crystals and the absence of mechanical damage are also important. ## Popular Localities Undoubtedly, the most sought-after and classic specimens come from the type locality – the Treasury Mine in Colorado, USA. Specimens from this location are considered exemplary for this mineral.
Care and storage
## Cleaning Treasuryite specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to its brittleness and potential for chemical reactions, avoid washing with water and any chemical agents. ## What to Avoid Avoid contact with chemicals, especially acids, which can damage it. The mineral is susceptible to oxidation, so it should be protected from moisture and airborne contaminants that can cause tarnishing. Also, avoid sudden temperature changes and mechanical shocks. ## Storage It is recommended to store treasuryite specimens in closed, dry containers or display cases with controlled atmospheres to minimize the risk of oxidation and tarnishing. Due to its softness, it should be stored separately from harder minerals to prevent scratching.