igneous
Pitted vesicular basalt, likely copper-stained
Basalt (mafic volcanic rock), possibly with secondary copper minerals such as chrysocolla or malachite
AI-generated identification · may be incorrectDark gray to reddish-brown, fine-grained and weathered, with abundant small vesicles; dull to earthy luster and no visible cleavage. Hardness is about 5–6 Mohs, with typical basalt specific gravity near 2.8–3.0.
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Physical properties
Dark gray to reddish-brown, fine-grained and weathered, with abundant small vesicles; dull to earthy luster and no visible cleavage. Hardness is about 5–6 Mohs, with typical basalt specific gravity near 2.8–3.0.
Formation & geological history
Formed when low-silica lava rapidly cooled at or near Earth’s surface; vesicles are gas bubbles preserved in the solidified lava. The blue-green coloration likely reflects later mineral staining or alteration, potentially from copper-bearing fluids; exact age cannot be determined visually.
Uses & applications
Common basalt is used as crushed aggregate, roadstone, riprap, and building stone. Attractive copper-stained pieces may be collected or used decoratively, but this specimen appears mainly of modest specimen value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms lava flows, dikes, and volcanic plateaus. Blue-green patches are not typical fresh basalt and may warrant an acid and streak test for identification of secondary minerals.
Field identification & locations
Look for fine grain, heavy weight, dark color, vesicles, and lack of quartz crystals; a steel nail generally does not scratch fresh basalt. Common locations include volcanic regions worldwide, including Hawaii, Iceland, the Pacific Northwest, and Mexico.
