Crerarite

Chemical formula: (Pt,Pb₂+)Bi₃(S₂-,Se₂-)₄-x (x = ₀.₄-₀-₈)

Crerarite is an extremely rare sulfide and selenide of platinum, lead, and bismuth, found as microscopic, metallic grains.

## Characteristics Crerarite is a member of the lillianite group, occurring as very small, anhedral to subhedral grains, usually not exceeding 100 micrometers in size. Due to its microscopic size, its visual features are difficult to observe without specialized equipment. It has a steel-gray color and a metallic luster. It most often occurs in intergrowths with other rare platinum-group minerals. ## Physical Properties This mineral is opaque. Its density, calculated based on chemical composition and unit cell parameters, is 8.61 g/cm³. Hardness has not been measured due to the small size of the grains. The luster is distinctly metallic. ## Colors and Varieties Crerarite is monochromatic – its color is described as steel-gray. No color varieties or commercial varieties are known. ## History and Name The mineral was approved by the IMA in 1991. Its name commemorates David A. Crerar (1946–1994), a geochemist from Princeton University, in recognition of his contributions to the study of noble metal geochemistry. It was described by a team of mineralogists led by L.J. Cabri based on material from the type locality. ## Uses Crerarite has no industrial application. Its significance is purely scientific and as a collector's item, of interest to specialized collectors of microscopic minerals.

Properties

Luster: Metallic
Streak: Black
Density: 8.61
Cleavage: None
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of crerarite with the naked eye or a hand lens is impossible. Definitive identification requires advanced analytical techniques, such as electron microprobe analysis (EMPA) to determine the exact chemical composition, and X-ray diffraction (XRD) to confirm the crystal structure. Under a microscope (in reflected light), it has a creamy white color. ## Distinguishing from Similar Minerals Crerarite can be confused with many other microscopic, metallic sulfides and tellurides of platinum-group metals, such as maslovite, kotulskite, moncheite, or pałovite, with which it often coexists. Differentiation relies solely on precise chemical analysis, which shows the simultaneous presence of platinum, lead, bismuth, sulfur, and selenium in characteristic proportions. ## Crystal Forms Crerarite forms only anhedral or subhedral grains. No well-formed crystals have been observed.

Geological environment

## Genesis Crerarite is a mineral of magmatic origin. It forms in the late stage of crystallization within pegmatitic gabbro dikes, associated with alkaline intrusive complexes. Its presence indicates specific geochemical conditions rich in platinum, bismuth, and semimetallic elements. ## Mineral Associations At the type locality, crerarite coexists with bornite, chalcopyrite, kotulskite, maslovite, michenerite, moncheite, pałovite, sopcheite, and an unnamed platinum-palladium bismuthotelluride. ## Localities The only confirmed occurrence of crerarite in the world is its type locality – the Coldwell alkaline complex near Marathon, Thunder Bay District, Ontario, Canada.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a crerarite specimen is not assessed based on aesthetics in the traditional sense. The most important criterion is the certainty of mineral identification, confirmed by analytical methods. The value of a specimen is enhanced by the abundance of its occurrence (the number of crerarite grains on the rock matrix) and the presence of rare associated minerals. Specimens from the type locality are the only ones available on the market. ## Popular Localities The most prized, and indeed the only known specimens, come from the Coldwell complex in Ontario, Canada.

Care and storage

## Cleaning Crerarite specimens are typically microscopic grains embedded in the host rock. Mechanical or chemical cleaning is impossible and inadvisable. The only safe method is to remove dust with a soft brush or a gentle stream of compressed air. ## What to Avoid Avoid contact with all chemicals, acids, and cleaning agents. Ultrasonic cleaners can damage delicate specimens and their associated minerals. High temperatures and sudden thermal changes should also be avoided. ## Storage Specimens containing crerarite should be stored in specialized "micromount" boxes, which protect them from dust, moisture, and mechanical damage. A label with precise locality information and identification confirmation is crucial.

Sources

IMA Mineral List (CNMNC)