Nickeltyrrellite
Chemical formula: Cu<sup>2+</sup>Ni<sup>3+</sup><sub>2</sub>Se<sup>2-</sup><sub>4</sub>
An extremely rare copper-nickel selenide of the linnaeite group, found as microscopic, metallic grains.
Description
## Characteristics Nickeltyrrellite is a very rare sulfide mineral belonging to the linnaeite group. It is the nickel analogue of tyrrellite. It occurs as microscopic, irregular grains, usually intergrown with other minerals, most often calcite. It does not form macroscopic crystals. On fresh surfaces, it has a metallic luster and a characteristic brownish-pink color. ## Physical Properties This mineral is opaque and exhibits a metallic luster. Its calculated density is 6.53 g/cm³, but its Mohs hardness has not yet been determined due to the small size of the grains. ## Colors and Varieties Nickeltyrrellite has a brownish-pink color; in reflected light under a microscope, it may show shades of light purplish-gray. No color or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1967 by D.C. Harris, refers to its chemical composition (dominance of nickel) and its relation to the structurally similar tyrrellite. Tyrrellite, in turn, was named after the Canadian geologist and explorer, Joseph Burr Tyrrell (1858–1957). The type locality is the Eagle mine in Saskatchewan, Canada. ## Applications Nickeltyrrellite has no industrial applications. Its significance is purely scientific and collectible, as a subject of interest for specialists in rare minerals and systematics.
Diagnostic features
## Identification Correct identification of nickeltyrrellite is impossible without advanced laboratory techniques. Due to its microscopic size and occurrence as inclusions, it requires chemical composition analysis (EDS/WDS) and crystal structure studies (XRD). ## Distinguishing from Similar Minerals It can be confused with other metallic minerals, especially tyrrellite (from which it differs by the dominance of nickel over cobalt), bornite (different chemical composition), and other selenide and sulfide ore minerals. Only chemical analysis provides a definitive distinction. ## Crystal Forms Nickeltyrrellite occurs exclusively as anhedral (irregular, poorly formed) grains of microscopic size. It often forms complex intergrowths with other selenides. No idiomorphic crystals are known.
Geological environment
## Genesis It is a low-temperature hydrothermal mineral. It forms in calcite-quartz veins cutting metamorphosed sandstones and gneisses. Its crystallization is associated with selenium mineralization processes. ## Mineral Associations Nickeltyrrellite co-occurs with a number of other, often rare, selenides, such as umangite, klockmannite, berzelianite, clausthalite, eskebornite, and tyrrellite. Native gold and calcite also accompany it. ## Localities The most important and type locality is the historic Eagle mine (Goldfields area) in Saskatchewan, Canada. This mineral has also been identified in the Czech Republic, in the Předbořice deposit near Kovářov.
Rarity
Extremely rare
Collector aspects
## Quality Criteria As a microscopic mineral, nickeltyrrellite is primarily valued by specialized collectors (so-called micromounters). The value of a specimen is determined by the richness of aggregates, confirmed identification through analysis, and the presence of rare associated minerals. Specimens without analytical confirmation have negligible value. ## Popular Localities The only source for obtaining collectible specimens is the historic type locality in Saskatchewan, Canada. Material from this location is extremely difficult to acquire.
Care and storage
## Cleaning Nickeltyrrellite specimens, which are typically micromounts, should not be wet cleaned. Any contaminants should be removed with extreme caution using a soft, dry brush or a stream of compressed air. ## What to Avoid As a selenide, the mineral is potentially susceptible to oxidation. Contact with moisture, water, and all chemicals should be avoided. Prolonged exposure to humid air can lead to its slow decomposition. ## Storage It is recommended to store specimens in a dry place, preferably in tightly sealed "perky box" containers, which protect against dust, moisture, and mechanical damage.