igneous
Weathered vesicular basalt (probable volcanic bomb)
Basalt, primarily plagioclase feldspar, pyroxene, and olivine
AI-generated identification · may be incorrectDark olive-gray, fine-grained, dull to slightly earthy luster, with abundant rounded vesicles and possible weathering pits; hardness about 5–6 Mohs, no obvious cleavage, typical specific gravity 2.7–3.1. The rounded shape suggests abrasion or an originally aerodynamic volcanic fragment.
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Physical properties
Dark olive-gray, fine-grained, dull to slightly earthy luster, with abundant rounded vesicles and possible weathering pits; hardness about 5–6 Mohs, no obvious cleavage, typical specific gravity 2.7–3.1. The rounded shape suggests abrasion or an originally aerodynamic volcanic fragment.
Formation & geological history
Formed when low-silica lava rapidly cooled, trapping gas bubbles; the surface may have weathered or been altered to greenish clay minerals. Basalt ranges from geologically ancient to modern, and volcanic bombs commonly form during explosive eruptions.
Uses & applications
Used as crushed stone, aggregate, ballast, and occasionally landscaping material; vesicular pieces are mainly collected as volcanic specimens rather than used for jewelry.
Geological facts
The holes are vesicles, not fossil burrows, though weathering can enlarge them. If unusually light and highly porous, pumice or scoria is an alternative, but this specimen appears relatively dense and basaltic.
Field identification & locations
Identify by its fine dark matrix, many gas cavities, and lack of sedimentary layering or crystal faces; common in volcanic regions, including Hawaii, Iceland, the western United States, and oceanic islands. A streak, density, and fresh broken surface would confirm it.
