igneous
Likely polished dark stone, possibly basalt
Basalt; fine-grained plagioclase–pyroxene rock (tentative identification)
AI-generated identification · may be incorrectDark brown-black, compact, and weakly glossy where polished or wet; typically hardness 6–7 Mohs, no visible crystals, and irregular fracture. The bright edge may reflect a polished surface or weathering rind.
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Physical properties
Dark brown-black, compact, and weakly glossy where polished or wet; typically hardness 6–7 Mohs, no visible crystals, and irregular fracture. The bright edge may reflect a polished surface or weathering rind.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Its age cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, road stone, building stone, and occasionally as a polished decorative or lapidary material.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly contains tiny plagioclase and pyroxene crystals invisible without magnification.
Field identification & locations
Confirm with a hand lens: basalt should be dense, fine-grained, and non-foliated; a streak test, magnet response, and fresh unpolished surface help distinguish it from slag, obsidian, or metal ore. Common sources include Hawaii, Iceland, India, and oceanic islands.
