igneous
Rounded river pebble, likely basaltic-andesite or andesite
Fine-grained volcanic rock; commonly plagioclase with pyroxene and/or hornblende, with possible iron-oxide alteration
AI-generated identification · may be incorrectBrown-gray, rounded and water-worn, dull to faintly earthy luster, fine-grained aphanitic texture, and no visible cleavage; hardness approximately 5.5–6.5 Mohs, specific gravity about 2.6–2.8.
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Physical properties
Brown-gray, rounded and water-worn, dull to faintly earthy luster, fine-grained aphanitic texture, and no visible cleavage; hardness approximately 5.5–6.5 Mohs, specific gravity about 2.6–2.8.
Formation & geological history
An extrusive igneous clast formed when lava cooled rapidly at or near Earth’s surface, then weathered and was rounded by stream or shoreline transport; its exact geological age cannot be determined from the image.
Uses & applications
Typically used as decorative landscaping stone, aquarium or craft material, and occasionally aggregate; this ordinary pebble has little jewelry value.
Geological facts
The smooth oval shape records prolonged abrasion during transport, while the uniform fine texture indicates rapid cooling rather than slow crystallization underground.
Field identification & locations
Common in volcanic terrains, river gravels, beaches, and glacial deposits worldwide. Field identification is supported by its dense, fine-grained texture, lack of layering or pores, and a dark streak or gray interior when freshly broken; exact identification requires a fresh surface or laboratory testing.
