igneous
Vesicular basalt pebble
Basalt, typically plagioclase–pyroxene–olivine with secondary iron oxides
AI-generated identification · may be incorrectDark brown, weathered surface with abundant rounded vesicles; dull to faintly glassy luster, fine-grained texture, no visible cleavage, Mohs hardness about 5–6, and specific gravity roughly 2.8–3.1.
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Physical properties
Dark brown, weathered surface with abundant rounded vesicles; dull to faintly glassy luster, fine-grained texture, no visible cleavage, Mohs hardness about 5–6, and specific gravity roughly 2.8–3.1.
Formation & geological history
An extrusive mafic igneous rock formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles. Its exact age is indeterminate from the image; such basalt occurs from Precambrian to recent volcanic settings.
Uses & applications
Common basalt is used as crushed aggregate, road stone, railway ballast, and building stone; small attractive pebbles have modest collecting or decorative value.
Geological facts
The holes are vesicles formed by escaping volcanic gases; later weathering or mineral deposition may enlarge or partly fill them. Brown coloration commonly reflects oxidation of iron-bearing minerals.
Field identification & locations
Identify it by its heavy, fine-grained dark body, irregular vesicles, and lack of layering or fossil structure; test with a steel knife and inspect a fresh broken surface. Common worldwide in volcanic regions, especially oceanic islands and flood-basalt provinces.
