igneous
Likely basalt (possibly iron-rich volcanic rock)
Basalt; predominantly plagioclase feldspar, pyroxene, and commonly olivine or iron oxides
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to slightly vitreous luster, usually massive with no visible cleavage; hardness about 5–6 Mohs and specific gravity roughly 2.8–3.0. The specimen appears rounded and weathered, but the image cannot confirm its exact mineralogy.
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Physical properties
Dark gray to black, fine-grained, dull to slightly vitreous luster, usually massive with no visible cleavage; hardness about 5–6 Mohs and specific gravity roughly 2.8–3.0. The specimen appears rounded and weathered, but the image cannot confirm its exact mineralogy.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic islands, and flood-basalt provinces. It may range from ancient Precambrian material to recently erupted lava.
Uses & applications
Used as crushed aggregate, roadstone, railway ballast, riprap, and occasionally building stone; attractive polished pieces are collected but are generally not gemstones.
Geological facts
Its dark color reflects abundant ferromagnesian minerals and iron-bearing oxides. Vesicles, if present, indicate gas bubbles trapped during cooling; none are clearly visible here.
Field identification & locations
Common worldwide, especially Hawaii, Iceland, oceanic crust, India’s Deccan Traps, and volcanic regions. A magnet may respond weakly to magnetite; a fresh broken surface should remain dark and fine-grained. Estimated value: $1–$10 for a common small specimen, usually more only if unusually textured or locality-labeled.
