Lillianite
Chemical formula: Pb²⁺₃-₂xAg¹⁺xBi³⁺₂+xS²⁻₆
Lillianite is a rare lead, bismuth, and silver sulfosalt, forming tabular or prismatic crystals with a metallic luster.
Properties
- Mohs hardness
- 2-3
- Color
- Steel grey
- Luster
- Metallic
- Streak
- Black
- Density
- 7
- Cleavage
- {100} very good, {010} less so, probably also {001}.
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Lillianite is identified by its steel-gray color, metallic luster, high density, and characteristic elongated or tabular crystals, often striated. Its softness (2-3 on the Mohs scale) is also an important diagnostic feature. It occurs in paragenesis with other sulfides and sulfosalts. ## Distinguishing from Similar Minerals Lillianite is sometimes confused with other lead and bismuth sulfosalts, such as galenobismutite, cosalite, or aikinite. Galena is more regular in form (cubic) and has perfect cleavage. Cosalite forms acicular or fibrous aggregates. Final differentiation often requires advanced analytical methods, such as EDS or XRD analysis. ## Crystal Forms Lillianite crystals are typically small, prismatic, elongated along one axis, or tabular. They often exhibit vertical striations on prismatic faces. It also occurs as granular aggregates, masses intergrown with other minerals, or as microscopic inclusions.
Geological environment
## Genesis Lillianite is a hydrothermal mineral, forming in ore veins under medium to high-temperature conditions. It occurs in polymetallic deposits, often associated with igneous rock intrusions. ## Mineral Associations It most commonly co-occurs with galena, quartz, pyrite, chalcopyrite, sphalerite, tetrahedrite, and other bismuth sulfosalts, such as cosalite, galenobismutite, and aikinite. Native bismuth may also accompany it. ## Localities Important worldwide localities include: the historical type locality in Leadville (Colorado, USA); Taxco mine (Mexico); Gladhammar (Sweden); Băița Bihor (Romania); Příbram (Czech Republic). It is also known from many other localities in Japan, Norway, and Canada, but rarely forms well-developed, large crystals there.
Rarity
Rare
For collectors
## Quality Criteria Most valued by collectors are specimens with well-formed, sharp, and undamaged crystals with a strong, metallic luster. Crystals with distinct striations, set on a contrasting quartz matrix, are particularly sought after. Crystal size is a key factor – specimens with crystals exceeding a centimeter are considered exceptional. ## Popular Localities The historical localities in Sweden (Gladhammar) and Romania (Băița Bihor) are considered classic and provide the best specimens. Specimens from these localities, although often from old collections, fetch the highest prices on the collector's market.
Care and storage
## Cleaning Lillianite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its softness, avoid any rubbing and hard tools. Wet cleaning is not recommended, and if necessary, use distilled water and immediately dry the specimen thoroughly. ## What to Avoid The mineral is sensitive to acids and other chemicals. Prolonged exposure to humid air can cause oxidation and dulling of its surface. Avoid ultrasonic cleaners and steam cleaners, which can damage the brittle crystals. ## Storage Lillianite is best stored in a closed, dry display box, away from other minerals that could scratch it. It is not sensitive to light, but limiting air exposure will slow down the dulling process.