igneous
Weathered dark igneous rock, likely basalt
Basalt; primarily plagioclase feldspar and pyroxene, commonly with olivine and iron oxides
AI-generated identification · may be incorrectTypically dark gray to brown-green, fine-grained, massive, and dull to slightly glassy; Mohs hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.8–3.1. The specimen appears rounded and weathered, with possible vesicles or altered mineral patches.
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Physical properties
Typically dark gray to brown-green, fine-grained, massive, and dull to slightly glassy; Mohs hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.8–3.1. The specimen appears rounded and weathered, with possible vesicles or altered mineral patches.
Formation & geological history
Basalt forms when low-silica magma cools rapidly at or near Earth’s surface, especially in volcanic flows and oceanic crust; most examples range from modern to Precambrian in age. Exact identification and age require thin-section or chemical analysis.
Uses & applications
Used extensively as crushed aggregate, road stone, railway ballast, riprap, and dimension stone; attractive polished pieces are occasionally collected but are not generally jewelry-grade.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the ocean floor. Greenish areas may reflect alteration of olivine or pyroxene to chlorite, serpentine, or other secondary minerals.
Field identification & locations
Identify it by its dark color, high density, fine texture, and lack of visible large crystals; a streak, magnet test, and fresh broken surface help distinguish it from slag or weathered gabbro. Common worldwide, especially volcanic regions and oceanic terrains.
