Sterryite
Chemical formula: Cu¹⁺(Ag¹⁺,Cu¹⁺)₃Pb²⁺₁₉(Sb³⁺,As³⁺)₂₂(As₂)⁴⁺S²⁻₅₆
Sterryite is a very rare, black sulfosalt of lead, silver, copper, antimony, and arsenic, occurring as fine, acicular crystals.
Properties
- Mohs hardness
- 3.5
- Luster
- Metallic
- Streak
- Black
- Density
- 0
- Cleavage
- Parallel to c
- Fracture
- Irregular/Uneven
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of sterryite is extremely difficult and impossible without advanced analytical methods, such as chemical composition analysis (EDS/WDS) and X-ray diffraction (XRD). In collecting conditions, identification relies on a label from a confirmed locality. A visual characteristic is its occurrence as black, tangled, acicular aggregates. ## Differentiation from Similar Minerals Sterryite is visually indistinguishable from many other rare lead sulfosalts, such as jamesonite, boulangerite, zinkenite, or other minerals from the sterryite group. All form similar, dark, acicular or fibrous aggregates. Certain differentiation requires specialized laboratory equipment. ## Crystal Forms Sterryite crystals are very small, elongated, and acicular, often with a cross-section below 10 micrometers. They typically form disordered, tangled, or felted aggregates in rock fissures.
Geological environment
## Genesis Sterryite is a hydrothermal mineral. It forms in the late stages of crystallization in ore veins, in an environment rich in lead, antimony, arsenic, and sulfur. In its type locality (Taylor Pit), it occurs in calcite veins cutting through marbles. ## Mineral Associations This mineral co-occurs with other sulfosalts and sulfides. In its type locality, it was found in association with jamesonite, madocite, laffittite, pyrite, sphalerite, chalcopyrite, galena, native arsenic, realgar, and orpiment, all within a calcite matrix. ## Localities The only confirmed and described locality for sterryite in the world is its discovery site – Taylor Pit, located near Madoc, Hastings County, Ontario, Canada.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a sterryite specimen primarily depends on the richness and visibility of the acicular crystal aggregates on the matrix. As it is a "micromount" type mineral, specimens are evaluated under a microscope. The most highly valued specimens are those with dense, well-formed crystal clusters, contrasting with a light host rock (e.g., calcite) and accompanied by other rare minerals. ## Popular Localities The only source of collector specimens is the historical type locality at Taylor Pit in Canada. This mine has long been inactive, and material on the market comes exclusively from old collections, making it extremely difficult to acquire.
Care and storage
## Cleaning Sterryite specimens should generally not be cleaned mechanically or chemically due to their brittleness and rarity. Fine, acicular crystals are extremely delicate. If necessary, dust can be removed very carefully with a soft brush or a photographic air blower. ## What to Avoid Avoid contact with all chemicals, acids, and detergents. The mineral is sensitive to oxidation, so it should be protected from moisture and sudden temperature changes. It should not be cleaned in ultrasonic cleaners. ## Storage Sterryite specimens are best stored in stable conditions, in closed, padded "micromount" boxes that protect them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight.