mineral

Michigan Float Copper

Native Copper (Cu)

Hardness: 2.5–3.0 on the Mohs scale. Color: Copper-red on fresh surfaces, weathering to green (malachite) or dark brown. Luster: Metallic. Crystal Structure: Isometric (cubic). Cleavage: None. Specific Gravity: 8.94 (very heavy).

Hardness: 2
Luster: Metallic

Identified February 11, 2026More mineral →

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Physical properties

Formation & geological history

Formed roughly 1.1 billion years ago during the Midcontinent Rift. Hydrothermal fluids deposited native copper into vesicles of basaltic lava and between conglomerate pebbles. 'Float' copper refers to pieces later ripped from the bedrock by Pleistocene glaciers and redeposited in glacial till.

Uses & applications

Historical source for electrical wiring and alloys; currently highly valued for geological display, lapidary art (bookends, cabochons), and museum specimens.

Geological facts

The Keweenaw Peninsula of Michigan is the only place on Earth where large-scale 'native' (pure) copper was commercially mined. These specimens can range from pebble-sized 'nuggets' to massive boulders weighing several tons.

Field identification & locations

Identify by its high density (feels much heavier than rock), copper-red color when scratched, and green oxidation (patina). Found in glacial till across the Upper Midwest, especially Michigan and Wisconsin. Use a metal detector for field hunting.