igneous
Weathered dark stone, possibly basalt
Basalt; commonly plagioclase feldspar, pyroxene, and minor olivine
AI-generated identification · may be incorrectFine-grained, dark gray-brown, dull to faintly earthy luster; likely Mohs 5–6, with no visible cleavage and relatively high density (about 2.8–3.0). The image alone cannot confirm composition; it may also be a dark sedimentary or metamorphic fragment.
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Physical properties
Fine-grained, dark gray-brown, dull to faintly earthy luster; likely Mohs 5–6, with no visible cleavage and relatively high density (about 2.8–3.0). The image alone cannot confirm composition; it may also be a dark sedimentary or metamorphic fragment.
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Most specimens are Cenozoic or younger, though basalt occurs throughout geological time.
Uses & applications
Used widely as crushed aggregate, road base, railroad ballast, riprap, and dimension stone; attractive polished pieces are used decoratively but this specimen appears common and unworked.
Geological facts
Its fine texture indicates rapid cooling, preventing large crystals from forming. A streak or scratch test, density, and close inspection for vesicles would improve identification.
Field identification & locations
Common worldwide, especially in Hawaii, Iceland, the Pacific Northwest, India’s Deccan Traps, and oceanic islands. Basalt is typically heavy, hard, and nonreactive with dilute acid; value is usually $1–$10 for an ordinary specimen.
