igneous
Weathered volcanic rock, likely basalt
Basalt; primarily plagioclase feldspar, pyroxene, and often olivine
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to subtly waxy luster, with reddish-brown weathering and possible vesicles or mineral-filled fractures. Hardness about 5–6 Mohs; massive, with no obvious cleavage and typically high specific gravity (~2.8–3.0).
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Physical properties
Dark gray-brown, fine-grained, dull to subtly waxy luster, with reddish-brown weathering and possible vesicles or mineral-filled fractures. Hardness about 5–6 Mohs; massive, with no obvious cleavage and typically high specific gravity (~2.8–3.0).
Formation & geological history
Formed when mafic lava rapidly cooled at or near Earth’s surface, commonly in oceanic or volcanic environments. The reddish coating reflects oxidation during prolonged weathering; exact age cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, road stone, riprap, and building stone; attractive polished pieces may be used decoratively. This rounded specimen has modest collecting value.
Geological facts
The rounded shape indicates abrasion by waves or river transport. Its surface appears strongly weathered, and the pale curving markings may be mineral veins, flow textures, or weathering patterns rather than fossils.
Field identification & locations
Common along volcanic coastlines, river beds, and glacial deposits. Confirm by examining a fresh broken surface: basalt should be uniformly fine-grained, heavy, and non-acid-reactive; a streak or hand lens can help distinguish it from altered sedimentary rock.
