igneous
Likely weathered basalt
Basalt; primarily plagioclase feldspar, pyroxene, and often olivine
AI-generated identification · may be incorrectDark gray-green, fine-grained and massive with dull to slightly waxy luster; individual crystals are poorly visible. Hardness about 5–6 Mohs, no prominent cleavage, and specific gravity roughly 2.8–3.0.
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Physical properties
Dark gray-green, fine-grained and massive with dull to slightly waxy luster; individual crystals are poorly visible. Hardness about 5–6 Mohs, no prominent cleavage, and specific gravity roughly 2.8–3.0.
Formation & geological history
An extrusive mafic igneous rock formed when basaltic lava cooled rapidly at or near Earth’s surface; its age cannot be determined from the photograph and may range from recent to billions of years.
Uses & applications
Commonly used as crushed aggregate, road material, riprap, and occasionally building or landscaping stone; ordinary pieces have little jewelry value.
Geological facts
The greenish coloration may reflect chlorite, epidote, or weathered olivine, and the pale spots could be feldspar or alteration minerals. The specimen could alternatively be a related greenstone, such as altered basalt.
Field identification & locations
Look for a dense, dark, fine-grained texture, weak magnetism, and absence of visible layering; a streak test, magnet, and fresh broken surface would improve identification. Basalt is widespread in oceanic crust and volcanic regions such as Hawaii, Iceland, India, and the Pacific Northwest.
