igneous
Iron-rich basalt or weathered volcanic rock
Likely altered basalt, composed mainly of plagioclase and pyroxene with iron oxides; exact identification requires testing
AI-generated identification · may be incorrectDark gray to brown, fine-grained and massive, with rusty red-brown weathering and metallic-looking specks. Likely hardness about 5–6, dull to submetallic luster, no obvious cleavage, and specific gravity roughly 2.8–3.3.
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Physical properties
Dark gray to brown, fine-grained and massive, with rusty red-brown weathering and metallic-looking specks. Likely hardness about 5–6, dull to submetallic luster, no obvious cleavage, and specific gravity roughly 2.8–3.3.
Formation & geological history
Formed when mafic lava cooled at or near Earth’s surface, probably in the Cenozoic or older; surface oxidation and hydrothermal alteration produced the rusty patches. The photograph alone cannot establish geological age.
Uses & applications
Common basalt is used as crushed aggregate, road stone, riprap, and occasionally dimension stone; attractive polished pieces may be collected, but this specimen does not visibly appear gem-grade.
Geological facts
The bright speckling could represent magnetite or other iron oxides, but metallic minerals cannot be confirmed visually. A magnet, streak test, and fresh broken surface would substantially improve identification.
Field identification & locations
Common in volcanic terrains worldwide, including oceanic crust and continental lava fields. Test for magnetic response, a gray-black streak, glassy versus granular texture, and reaction to dilute acid; a thin section or laboratory analysis may distinguish basalt from iron-rich slag or ore.
