igneous
Weathered river stones, likely basaltic andesite and related volcanic rocks
Fine-grained mafic/intermediate volcanic rocks; commonly basalt (plagioclase + pyroxene ± olivine) or andesite (plagioclase + pyroxene ± amphibole)
AI-generated identification · may be incorrectRounded, water-worn specimens with dull earthy luster, gray-green to brown weathering, and very fine-grained texture; typical hardness is about 5–6 Mohs, with no visible cleavage or large crystals. Exact identification requires a fresh broken surface or testing.
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Physical properties
Rounded, water-worn specimens with dull earthy luster, gray-green to brown weathering, and very fine-grained texture; typical hardness is about 5–6 Mohs, with no visible cleavage or large crystals. Exact identification requires a fresh broken surface or testing.
Formation & geological history
Formed when lava cooled rapidly at or near Earth’s surface, then was transported and rounded by stream or coastal erosion; ages may range from recent to hundreds of millions of years depending on locality.
Uses & applications
Commonly used as landscaping stone, aggregate, road material, and erosion-control rock; attractive pieces may be used as hand specimens or decorative stones.
Geological facts
The green coloration may reflect chlorite, epidote, or other alteration minerals replacing original volcanic minerals. The image shows a collection rather than one uniquely identifiable specimen.
Field identification & locations
Look for a dense, fine-grained interior, weak magnetism in some basalt, and abundant rounded surfaces; streak, acid, magnet, and hardness tests help distinguish basalt from andesite or altered rock. Common worldwide near volcanic terrains and river gravels.
