igneous
Chalcopyrite in River Pebble (Pebble with Pyrite/Fool's Gold inclusions)
CuFeS2 in fine-grained igneous host rock (Basalt / Andesite)
Hardness: 3.5-4 for chalcopyrite spots, 6-6.5 for matrix; Color: Dark grey to black matrix with brassy yellow to golden-orange metallic flecks; Luster: Metallic flecks on dull/earthy matrix; Cleavage: Poor
- Hardness
- 3
- Luster
- Metallic flecks on dull/earthy matrix
Identified More igneous →
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Physical properties
Hardness: 3.5-4 for chalcopyrite spots, 6-6.5 for matrix; Color: Dark grey to black matrix with brassy yellow to golden-orange metallic flecks; Luster: Metallic flecks on dull/earthy matrix; Cleavage: Poor
Formation & geological history
Formed in igneous or hydrothermal environments where copper-iron sulfide minerals crystallized within mafic host rock. Subsequently eroded and rounded by stream or beach water into a smooth river pebble.
Uses & applications
Copper ore in massive quantities; individual water-worn pebbles like this are primarily novelty educational specimens or beachcombing finds.
Geological facts
Golden metallic spots in river pebbles are often mistaken for real gold. However, real gold is malleable and does not oxidize or rust, whereas iron and copper sulfides like chalcopyrite or pyrite often show orange limonite weathering halos.
Field identification & locations
Look for dark, water-worn pebbles with metallic brassy-yellow specks that show slight orange rust/limonite staining upon exposure to moisture and air. Commonly found along riverbeds, beaches, and gravel deposits.
