Nordströmite
Chemical formula: Pb<sup>2+</sup><sub>3</sub>Cu<sup>1+</sup>Bi<sup>3+</sup><sub>7</sub>(S<sup>2-</sup>,Se<sup>2-</sup>)<sub>14</sub>
Nordströmite is a rare copper, lead, and bismuth sulfoselenide, forming small, metallic-lustered crystals.
Description
## Characteristics Nordströmite is a rare mineral from the sulfosalt group, chemically classified as a copper, lead, and bismuth sulfoselenide. It occurs as small, bladed or acicular crystals, rarely exceeding 1 mm in length. These crystals often form tangled or radial aggregates. The mineral has a characteristic metallic luster and a steel-gray to tin-white color, which may develop a darker tarnish over time. ## Physical Properties The Mohs hardness of nordströmite is approximately 3.5, making it a relatively soft mineral. It is opaque and heavy, with a density of 7.15 g/cm³, which is typical for minerals containing lead and bismuth. It exhibits good cleavage in one direction. ## Colors and Varieties This mineral is typically steel-gray, tin-white, or grayish-black. A dull, dark tarnish may form on its surface due to weathering processes. No distinct color varieties or commercial varieties are recognized. ## History and Name Nordströmite was first described in 1979 by S. Karup-Møller. The mineral is named in honor of Thomas F. W. Nordström (1851-1936), a Swedish mining engineer and geologist who contributed to the study of Swedish ore deposits. ## Uses Due to its rarity and occurrence in small quantities, nordströmite has no industrial applications. It is solely an object of scientific interest and is valued by advanced mineral collectors.
Diagnostic features
## Identification Helpful features for identifying nordströmite include its metallic luster, steel-gray color, high density, and characteristic small, bladed crystals. It often occurs in association with other bismuth minerals. However, definitive identification is difficult without advanced analytical methods, such as chemical composition analysis (EDS) or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Nordströmite can be easily confused with other gray, metallic sulfosalts, such as bismuthinite, cosalite, aikinite, or lillianite. Distinguishing them based on visual characteristics is often impossible. Chemical tests, and sometimes detailed observation of crystal forms under a microscope, are crucial for differentiation. ## Crystal Forms It forms elongated, bladed or acicular crystals, often flattened. They usually occur as disordered or radial aggregates and intergrowths within other minerals.
Geological environment
## Genesis Nordströmite is a hydrothermal mineral. It forms in ore veins, particularly within metamorphic rocks, such as skarns, that have undergone bismuth mineralization. ## Mineral Associations It most commonly co-occurs with other ore minerals, especially native bismuth, bismuthinite, cosalite, galena, chalcopyrite, and other rare lead and bismuth sulfosalts. ## Localities Key and classic localities for this mineral include: - Björkskogsnäs Mine in Hällefors (Örebro, Sweden) - type locality. - Gladhammar Mines near Västervik (Kalmar, Sweden). - Băița Bihorului deposit (formerly Rézbánya) in Romania. - Nagybörzsöny district in Hungary.
Rarity
Very rare
Collector aspects
## Quality Criteria For collectors, specimens with well-formed, sharp microcrystals, ideally forming aesthetic aggregates, are most valuable. Rich associations with other rare minerals, especially native bismuth, are also highly prized. Due to the nature of the mineral, crystal size is secondary – their quality and abundance on the rock matrix are key. ## Popular Localities The most valued collector specimens come from historical localities in Sweden (Björkskogsnäs, Gladhammar) and from the Romanian Băița Bihorului deposit, where rich concentrations of this mineral are known.
Care and storage
## Cleaning Nordströmite specimens should only be dry-cleaned using a soft brush to remove dust. Avoid contact with water and any chemical agents, as they can cause damage or tarnishing. ## What to Avoid The mineral is sensitive to moisture, which can accelerate oxidation processes and tarnish formation. It should be protected from acids and other chemicals. It is also soft and brittle, so impacts, scratches, and ultrasonic cleaning should be avoided. ## Storage It is recommended to store specimens in a dry place, preferably in a closed, airtight container (e.g., a “perky box”), to limit air and moisture exposure. Protect from dust and direct contact with other minerals that could scratch it.