igneous
Likely weathered basalt or dark volcanic rock
Basalt; primarily plagioclase feldspar and pyroxene, with possible olivine and iron oxides
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to weakly vitreous luster, irregular fracture, and typically Mohs hardness 6–7. The elongated, rounded form appears naturally weathered or water-worn; metallic-looking patches may be iron staining or reflective mineral grains.
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Physical properties
Dark gray to black, fine-grained, dull to weakly vitreous luster, irregular fracture, and typically Mohs hardness 6–7. The elongated, rounded form appears naturally weathered or water-worn; metallic-looking patches may be iron staining or reflective mineral grains.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Its age cannot be determined from the image and may range from very recent to billions of years old.
Uses & applications
Used as crushed aggregate, roadstone, railroad ballast, building stone, and occasionally as polished decorative material. Common pieces have little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. It can resemble andesite, slag, or meteorite material, so identification is provisional without a fresh surface, streak, density, and magnetic tests.
Field identification & locations
Common worldwide, especially Hawaii, Iceland, the Pacific Northwest, India’s Deccan Traps, and oceanic regions. A genuine specimen is usually dense, nonporous, weakly magnetic, and lacks obvious metallic fusion crust; testing with a magnet and examining a broken edge helps.
