Auricupride

Chemical formula: Cu<sub>3</sub>Au

A naturally occurring alloy of gold and copper, forming a continuous solid solution with pure copper and gold.

## Characteristics Auricupride is a rare alloy of copper and gold, belonging to the native elements group. Its chemical composition corresponds to the formula Cu₃Au. It rarely forms distinct crystals, most often occurring as irregular grains, flakes, dendrites, or masses intergrown with other minerals, primarily native copper. Its appearance is metallic, and its color varies depending on the gold-to-copper ratio. ## Physical Properties Auricupride is a malleable and ductile mineral, typical of metal alloys. It is characterized by a strong metallic luster. Its Mohs hardness is 3-3.5, and its density is high, ranging from 11.5 to 13.5 g/cm³, depending on the exact chemical composition. ## Colors and Varieties The color of auricupride is characteristic and depends on its gold content. Typically, it ranges from coppery-red to yellow. A variety with a composition close to AuCu is known as rosetine (or tetra-auricupride), and a variety with a composition of Au₂Cu₃ is sometimes called cuproaurite. However, these names are not universally accepted as distinct mineral species. ## History and Name The name auricupride, given in 1950 by Paul Ramdohr, comes from the Latin words *aurum* (gold) and *cuprum* (copper), which directly refers to its chemical composition. However, the mineral was known and studied earlier, and its first formal publication (without a name) dates back to 1939 based on material from the Urals in Russia. ## Uses Due to its rarity, auricupride has no industrial applications. However, it is a valued collector's mineral, sought after for its unique composition and origin.

Properties

Mohs hardness
3-3.5
Luster
Metallic
Streak
Reddish-yellow
Density
11.5 - 13.5
Cleavage
None
Fracture
Hackly
Transparency
Opaque
Crystal system
Cubic

Diagnostic features

## Identification Auricupride is identified by its metallic luster, characteristic coppery-red to yellow color, and high density. It is malleable and ductile. It often occurs in paragenesis with native copper, which is an important diagnostic clue. ## Distinguishing from Similar Minerals It can be confused with native copper, which, however, has a more uniform, red color and often develops a green patina. Native gold is much yellower and denser. Accurate identification requires advanced methods such as chemical analysis (EDS) or X-ray diffraction (XRD). ## Crystal Forms Crystals are extremely rare and usually have a simple, regular form. Most commonly found are granular aggregates, dendritic forms, flakes, and irregular masses intergrown in the host rock or other minerals.

Geological environment

## Genesis Auricupride forms through hydrothermal processes in serpentinites and in the oxidation zones of copper sulfide deposits. It forms under conditions of low sulfur activity. It can also form through metamorphic processes. ## Mineral Associations It most commonly co-occurs with native copper, native gold, platinum, chalcopyrite, magnetite, chromite, and also with minerals from the platinum group. ## Localities The most important localities worldwide include the Urals in Russia (which is the type locality), the Sudbury region in Canada, as well as occurrences in China, South Africa, Australia, Finland, and Chile.

Rarity

Rare

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, though rare, crystals or distinct dendritic forms. Rich intergrowths of auricupride in native copper, creating visually attractive compositions, are also highly valued. The intensity and hue of the color also influence the specimen's value. ## Popular Localities Specimens from classic localities, such as the Urals in Russia, are historically important and sought after. Material from Canada and South Africa is also present in collections worldwide.

Care and storage

## Cleaning Dry cleaning using a soft brush or compressed air is recommended to remove dust. Avoid contact with water, especially if the specimen contains associated minerals sensitive to moisture. ## What to Avoid Avoid contact with acids and strong chemicals, which can react with copper. Prolonged exposure to humid air can cause superficial oxidation and tarnishing of the surface. Protect from scratching by harder minerals. ## Storage Specimens should be stored in a dry place, preferably in sealed boxes or display cases, to limit air and moisture exposure. It is advisable to separate it from other minerals to prevent mutual scratching.

External references

Sources

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