igneous
Dark gray river pebble, likely basalt or fine-grained metamorphic stone
Probable basalt (plagioclase–pyroxene aggregate); exact identification is uncertain from the photograph
AI-generated identification · may be incorrectSmooth, water-worn, dense, fine-grained, and dark gray-green with a dull to slightly satin luster; basalt typically has Mohs hardness 5–6, no visible cleavage, and specific gravity about 2.8–3.0. The specimen appears rounded and flattened from abrasion.
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Physical properties
Smooth, water-worn, dense, fine-grained, and dark gray-green with a dull to slightly satin luster; basalt typically has Mohs hardness 5–6, no visible cleavage, and specific gravity about 2.8–3.0. The specimen appears rounded and flattened from abrasion.
Formation & geological history
Likely formed as volcanic basalt from rapidly cooled mafic lava, then transported and polished by stream or shoreline erosion; its exact geological age cannot be determined visually. If metamorphic, a possible alternative is greenstone or fine-grained slate.
Uses & applications
Common basalt is used as aggregate, paving stone, and occasionally as a decorative or landscape stone; this small pebble has mainly educational or personal-collection value.
Geological facts
Basalt is the most common volcanic rock on Earth and forms much of the oceanic crust. Its dark color reflects iron- and magnesium-rich minerals.
Field identification & locations
Look for a uniformly fine texture, high density, dark color, and possible tiny plagioclase crystals; a streak, magnetism, hardness, and thin-section test would improve identification. Common in river gravels and beaches worldwide.
