man-made alloy (metallic)

Nickel coin (U.S. currency)

Cupronickel (75% Copper, 25% Nickel alloy)

Hardness: 5-5.5 (Mohs); Color: Silvery-white to grey; Luster: Metallic; Crystal structure: Face-centered cubic (FCC) at the atomic level; Cleavage: None (malleable/ductile); Specific Gravity: ~8.9

Hardness: 5-5
Color: Silvery-white to grey
Luster: Metallic

Identified March 29, 2026More man-made alloy (metallic) →

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Physical properties

Hardness: 5-5.5 (Mohs); Color: Silvery-white to grey; Luster: Metallic; Crystal structure: Face-centered cubic (FCC) at the atomic level; Cleavage: None (malleable/ductile); Specific Gravity: ~8.9

Formation & geological history

Produced via mining of nickel-bearing ores (like pentlandite) and copper ores (like chalcopyrite), followed by industrial smelting and alloying. The Jefferson Nickel design has been used since 1938.

Uses & applications

Legal tender/currency. In a geological context, coins are often used as a 'scale of reference' for photographing actual rocks and minerals.

Geological facts

This particular coin appears to be a U.S. Jefferson Nickel. Prior to 1938, the U.S. produced the 'Buffalo' nickel. During WWII (1942-1945), nickels were made of silver, copper, and manganese because nickel was needed for the war effort.

Field identification & locations

In the field, geologists use coins or pocket knives to test the hardness of unidentified minerals. A nickel can help differentiate between minerals softer or harder than 5 on the Mohs scale. Found globally in circulation.

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One Pound Coin (UK)

Nickel-Brass Alloy (Cu-Zn-Ni)

mineral

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Ferrous Alloy containing Iron (Fe), Chromium (Cr), and Carbon (C)

Mineral equivalent / Metal Alloy

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Titanium-anodized or electroplated alloy (e.g., Ti-coated Zinc or Aluminum)

Mineral alternative / Synthetic

Metal Alloy (Likely Pewter or Sterling Silver)

Not a natural geological specimen; composed of refined metals. If pewter, it's a tin-based alloy. If sterling silver, it's 92.5% silver and 7.5% other metals (usually copper).

Man-made material (metal)

Transit Token (RTD Denver)

Nickel-plated brass or bronze alloy (Cu-Sn-Zn-Ni)

not a rock or mineral (anthropogenic material)

Ferrochrome Slag

Anthropogenic slag (Fe-Cr alloy waste)

industrial byproduct