Nuffieldite
Chemical formula: Pb<sup>2+</sup><sub>2</sub>Cu<sup>1+</sup><sub>1.4</sub>(Pb<sup>2+</sup><sub>0.4</sub>Bi<sup>3+</sup><sub>0.4</sub>Sb<sup>3+</sup><sub>0.2</sub>)Bi<sup>3+</sup><sub>2</sub>S<sup>2-</sup><sub>7</sub>
An extremely rare lead-copper-bismuth sulfosalt with a metallic luster, forming small, acicular crystals.
Properties
- Mohs hardness
- 2.5
- Luster
- Metallic
- Streak
- Black
- Density
- 7.04
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Identification of nuffieldite in the field is practically impossible without specialized equipment. In a collection, it can be preliminarily recognized by its lead-gray color, metallic luster, and characteristic, small, acicular crystals, often forming aggregates. However, definitive identification requires advanced analytical methods, such as chemical composition analysis (EDS) or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Nuffieldite can be confused with many other sulfosalts of similar appearance, such as aikinite, bismuthinite, jamesonite, or other rare sulfosalts from the aikinite group. Distinguishing it from these minerals based on visual characteristics is unreliable and requires specialized laboratory tests. ## Crystal Forms Nuffieldite forms elongated, prismatic, or acicular crystals, often with a square or rectangular cross-section. These crystals usually occur as radial or tangled clusters and aggregates. Single, well-formed crystals are rarely found.
Geological environment
## Genesis Nuffieldite is a hydrothermal mineral. It forms in quartz veins that cut altered volcanic rocks (andesites). It crystallizes under relatively low-temperature conditions from solutions rich in lead, copper, bismuth, antimony, and sulfur. ## Mineral Associations This mineral coexists with other sulfides and sulfosalts. In its type locality (Alice Arm, British Columbia, Canada), it has been found in association with aikinite, bismuthinite, cassiterite, covellite, matildite, pyrite, sphalerite, chalcopyrite, and quartz. ## Localities Nuffieldite is an extremely rare mineral, known from only a few localities worldwide. The most important ones include: * **Canada** - Alice Arm in British Columbia (type locality). * **Sweden** - Falun mine in the Dalarna region. * **Japan** - Iimori mine in Wakayama Prefecture.
Rarity
Extremely rare
For collectors
## Quality Criteria Due to the extreme rarity and microscopic size of its crystals, any authenticated nuffieldite specimen is valuable to specialized collectors. The most highly prized specimens are those that display well-formed, even if tiny, acicular crystals, preferably in association with other rare minerals. The richness of the aggregates and the contrast with the matrix mineral (e.g., quartz) enhance the visual and collectible value of the specimen. ## Popular Localities By far the most desirable and historically significant locality is the type locality in Alice Arm, Canada. Specimens from this location are classics and serve as a benchmark for this mineral.
Care and storage
## Cleaning Nuffieldite specimens are extremely delicate and rare, so their cleaning should be limited to an absolute minimum. If necessary, compressed air (from a safe distance) can be used to remove loose dust. Any contact with water or chemical agents should be avoided. ## What to Avoid Contact with water, acids, bases, and all solvents must be strictly avoided. The mineral is soft and brittle, susceptible to mechanical damage. It should not be heated or exposed to ultrasound. Prolonged exposure to humid air can lead to its slow oxidation. ## Storage Specimens should be stored in a dry, stable environment, preferably in a sealed collector's box (e.g., a "micromount" box), to protect them from dust, moisture, and mechanical damage. Due to its lead content, hands should be washed after any contact with the mineral.