mineral

Cupronickel (on a 1981 Mexico 20 Pesos coin)

Copper-Nickel Alloy (Cu75Ni25)

Color: Dull silver-grey; Hardness: 3.5 on Mohs scale (alloyed); Luster: Metallic; Structure: Face-centered cubic; Streak: Metallic grey; Non-magnetic.

Hardness: 3
Color: Dull silver-grey
Luster: Metallic

Identified March 18, 2026More mineral →

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Physical properties

Color: Dull silver-grey; Hardness: 3.5 on Mohs scale (alloyed); Luster: Metallic; Structure: Face-centered cubic; Streak: Metallic grey; Non-magnetic.

Formation & geological history

Anthropogenic geological material. Formed through industrial smelting and alloying of copper (Cu) and nickel (Ni) ores. Natural nickel-copper sulfides often found in mafic and ultramafic igneous complexes.

Uses & applications

Primarily used for high-circulation coinage, marine hardware, and heat exchangers due to its excellent corrosion resistance in seawater and high durability.

Geological facts

The image features a 1981 Mexican 20 Pesos coin depicting a Chichen Itza Mayan ball player. Though cupronickel is common, this specific alloy has been used in coinage since the mid-19th century.

Field identification & locations

Identified in the field by its silver-like appearance but lack of magnetic pull and resistance to oxidation (patina is usually dull grey rather than black silver sulfide). Common in urban areas as currency.

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