igneous
Likely tumbled basalt or dark river stone
Basalt; predominantly plagioclase and pyroxene, possibly with olivine
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to weakly waxy luster, rounded and smoothly weathered; typical hardness about 5–6 Mohs and specific gravity about 2.8–3.1. The image is insufficient to confirm crystal texture or cleavage.
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Physical properties
Dark gray-green, fine-grained, dull to weakly waxy luster, rounded and smoothly weathered; typical hardness about 5–6 Mohs and specific gravity about 2.8–3.1. The image is insufficient to confirm crystal texture or cleavage.
Formation & geological history
Likely formed from rapidly cooled mafic lava, commonly Cenozoic to Precambrian in age, then rounded by stream or beach transport; it may also be a commercially tumbled landscaping stone.
Uses & applications
Used as aggregate, road stone, riprap, and decorative rock; ordinary pieces have little jewelry value.
Geological facts
Basalt is Earth’s most widespread volcanic rock and forms much of the oceanic crust. Greenish tones may reflect altered pyroxene or olivine minerals.
Field identification & locations
Identify with a fresh surface, strong density, fine texture, and absence of visible quartz; a streak test is usually gray, and a magnet may show weak attraction if iron-bearing. Common in volcanic regions and gravel beds.
