igneous
Dark volcanic rock, likely basalt
Basalt (fine-grained mafic volcanic rock; exact identification requires testing)
AI-generated identification · may be incorrectDark gray to black, dull to slightly lustrous, with a fine-grained surface and a few pale inclusions or mineral-filled seams. Basalt’s main minerals are plagioclase and pyroxene, commonly with olivine; hardness is roughly 5–6 Mohs, and its crystals are usually too small to see clearly.
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Physical properties
Dark gray to black, dull to slightly lustrous, with a fine-grained surface and a few pale inclusions or mineral-filled seams. Basalt’s main minerals are plagioclase and pyroxene, commonly with olivine; hardness is roughly 5–6 Mohs, and its crystals are usually too small to see clearly.
Formation & geological history
Likely formed when low-silica lava cooled at or near Earth’s surface; basalt ranges from very young flows to ancient rocks found in oceanic crust and flood-basalt provinces.
Uses & applications
Basalt is widely used as crushed aggregate, road stone, and construction material; this rounded specimen is mainly suitable for collecting or display.
Geological facts
The rounded shape may result from stream or beach abrasion, but the photo alone cannot establish where it formed or whether it is basalt rather than another dark rock.
Field identification & locations
Check for a dense, fine-grained texture and pale plagioclase; a streak, magnetism, fresh broken surface, and mineral examination can help distinguish basalt from slag or other dark rocks. Basalt is common worldwide, especially in volcanic regions and oceanic crust.
