Hammarite
Chemical formula: Cu<sup>1+</sup><sub>2</sub>Pb<sup>2+</sup><sub>2</sub>Bi<sup>3+</sup><sub>4</sub>S<sup>2-</sup><sub>9</sub>
A very rare copper, lead, and bismuth sulfosalt, forming acicular or prismatic crystals with a metallic luster.
Properties
- Mohs hardness
- 4
- Luster
- Metallic
- Streak
- Black
- Density
- 6.63
- Cleavage
- None
- Fracture
- Uneven to subconchoidal
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Identifying hammarite under amateur conditions is very difficult. Helpful characteristics include its steel-gray color, metallic luster, high density, and acicular or slender prismatic crystal habit. However, the key is the environment of occurrence – the presence of other bismuth minerals. ## Distinguishing from Similar Minerals Hammarite is visually almost impossible to distinguish from other rare bismuth sulfosalts, such as aikinite, lindstromite, gladite, or bismuthinite. All these minerals have similar color, luster, and habit. Definitive distinction requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS). ## Crystal Forms Hammarite crystals are most often elongated, prismatic, or acicular. They usually occur as inclusions in other minerals, forming chaotic aggregates or radial groupings. Less commonly, it is found in massive or granular forms.
Geological environment
## Genesis Hammarite is a hydrothermal mineral. It forms under high-temperature conditions, in ore veins associated with intrusions of igneous rocks, most often granitoids. ## Mineral Associations It most commonly co-occurs with other bismuth sulfosalts, especially from the aikinite-bismuthinite series (e.g., aikinite, lindstromite). It is also accompanied by chalcopyrite, pyrite, bismuthinite, quartz, and sometimes gold. ## Localities The most important occurrences of this mineral worldwide are few. Besides the type locality in Gladhammar, Sweden, it is known from Băița Bihor in Romania, the San Francisco mine in Argentina, and also from several localities in Arizona and Colorado (USA) and Queensland (Australia).
Rarity
Very rare
For collectors
## Quality Criteria The most highly valued by collectors are specimens with well-formed, isolated crystals, which is extremely rare. The value of a specimen is also enhanced by a rich association with other rare minerals, especially if they form aesthetic compositions. Most specimens available on the market are microscopic inclusions or small granular aggregates. ## Popular Localities Historical specimens from the type locality – the Gladhammar mine in Sweden – are considered classic and most desirable. Material from this locality is of greatest importance to specialized collectors.
Care and storage
## Cleaning Hammarite specimens should be cleaned very carefully, preferably with a soft brush dry. If necessary, distilled water can be used, but the specimen should be thoroughly dried immediately. Ultrasonic cleaners should be avoided, as they can damage delicate crystals. ## What to Avoid Hammarite is a soft and brittle mineral, susceptible to scratches and mechanical damage. As a sulfide, it is sensitive to acids and other aggressive chemicals. Prolonged exposure to humid air can cause its oxidation and the formation of tarnish. ## Storage It is recommended to store specimens in a dry place, in closed boxes or display cases, to limit air and moisture access, which will slow down the oxidation process. Protect from dust and mechanical damage.