Nowackiite
Chemical formula: Cu<sup>1+</sup><sub>6</sub>Zn<sup>2+</sup><sub>3</sub>As<sup>3+</sup><sub>4</sub>S<sup>2-</sup><sub>12</sub>
A very rare copper, zinc, and arsenic sulfosalt, forming microscopic, steel-gray crystals in dolomites of the Swiss Binn Valley.
Description
## Characteristics Nowackiite is a complex arsenic, copper, and zinc sulfosalt, belonging to a group of very rare minerals. It occurs as extremely small, usually sub-millimeter rhombohedral crystals or as granular, massive aggregates. Its color is steel-gray to lead-gray, often with a bluish or iridescent tarnish resulting from oxidation. Due to the size of its crystals, it is a typical micromount mineral, impossible to evaluate with the naked eye. ## Physical Properties This mineral is characterized by a metallic luster and is completely opaque. Its Mohs hardness is approximately 3, making it relatively soft. The density calculated from the chemical formula and unit cell parameters is 4.55 g/cm³. ## Colors and Varieties Nowackiite is uniform in color, ranging from steel-gray to lead-gray. The surface of the crystals may be covered with a characteristic bluish tarnish. No color varieties or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Werner Nowacki (1909–1988), a professor of crystallography at the University of Bern, Switzerland, who made significant contributions to the study of sulfosalts from the Binn Valley. Nowackiite was first described in 1965 after its discovery in the Lengenbach quarry in Switzerland, which remains its type locality. ## Uses Due to its extreme rarity and microscopic size, nowackiite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for specialized collectors of rare minerals.
Diagnostic features
## Identification Identification of nowackiite is extremely difficult and impossible to perform based on visual characteristics in field or amateur conditions. Its steel-gray color and metallic luster are typical of many sulfosalts. Certain identification requires advanced analytical techniques, such as X-ray diffraction (XRD) or X-ray microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Nowackiite can be confused with numerous other rare sulfosalts found in the same locality (Lengenbach quarry), such as baumhauerite, dufrénoysite, rathite, sartorite, or tennantite. All these minerals form small, gray crystals with a metallic luster. The differences between them are subtle, concerning crystal symmetry and chemical composition, which makes visual differentiation impossible. ## Crystal Forms Nowackiite crystals are very small, usually not exceeding 0.5 mm. They take the form of rhombohedra, often imperfectly formed and distorted. They usually form granular aggregates and clusters growing on other minerals, mainly on dolomite.
Geological environment
## Genesis Nowackiite forms as a result of low-temperature hydrothermal processes. It occurs in cavities and fissures of metamorphosed, saccharoidal Triassic dolomites. Its formation is associated with the activity of solutions rich in sulfur, arsenic, copper, and zinc. ## Mineral Associations This mineral co-occurs with a rich assemblage of other, often rare sulfosalts and sulfides. The most common associated minerals include sphalerite, pyrite, tennantite, as well as other arsenic sulfosalts such as jordanite, rathite, baumhauerite, and trechmannite. ## Localities The only confirmed and significant occurrence of nowackiite in the world is its type locality – the Lengenbach quarry, located in the Binn Valley (Binntal) in the canton of Valais, Switzerland. This site is renowned for its exceptional accumulation of rare sulfur-bearing minerals.
Rarity
Very rare
Collector aspects
## Quality Criteria The quality of nowackiite specimens, being a micromount mineral, is evaluated according to different criteria than for cabinet specimens. Samples with sharp, well-formed microcrystals that are clearly visible on the rock matrix are most highly valued. Additional value is provided by a rich association with other rare sulfosalts from Lengenbach, especially if they are well-identified. ## Popular Localities For collectors seeking nowackiite, the only source is the Lengenbach quarry in Switzerland. Specimens from this location are considered classic and most desirable.
Care and storage
## Cleaning Nowackiite specimens are almost exclusively microminerals, which are very delicate. Only a photographic air blower should be used to remove dust. Any contact with water or chemical agents is discouraged. Mechanical cleaning, even with a soft brush, risks damaging the microscopic crystals. ## What to Avoid Moisture should be avoided, as it can accelerate oxidation processes and the formation of tarnish on the surface. The mineral is sensitive to acids and other chemical reagents. As an arsenic sulfosalt, mineral dust is toxic – any actions that could lead to its formation should be avoided. ## Storage Specimens should be stored in specialized micromount boxes that protect them from dust, moisture, and mechanical damage. It is recommended to store them in stable conditions, away from direct sunlight and heat sources.