igneous
Dark volcanic rock, likely basalt
Basalt; primarily plagioclase feldspar, pyroxene, and often olivine
AI-generated identification · may be incorrectFine-grained, dark gray to black, dull to subtly vitreous luster, typically massive with no visible cleavage; Mohs hardness about 5–6 and specific gravity roughly 2.8–3.0. The rounded shape may reflect natural weathering or tumbling.
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Physical properties
Fine-grained, dark gray to black, dull to subtly vitreous luster, typically massive with no visible cleavage; Mohs hardness about 5–6 and specific gravity roughly 2.8–3.0. The rounded shape may reflect natural weathering or tumbling.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, lava flows, and volcanic islands. Most examples are geologically young, though basalt occurs throughout Earth’s history.
Uses & applications
Used as crushed aggregate, road stone, railroad ballast, building stone, and occasionally in landscaping or polished decorative objects; ordinary specimens have minimal jewelry value.
Geological facts
Its very fine texture indicates rapid cooling, unlike coarse-grained granite. Vesicles, if present, would indicate gas bubbles in the original lava, but none are clearly visible here.
Field identification & locations
Identify it by its black, dense, fine-grained appearance and lack of obvious crystals; a streak, density, and fresh broken surface would help confirm basalt over slag or other dark rocks. Common worldwide, especially near volcanic regions.
