igneous
Polished volcanic basalt pebble
Basalt, chiefly plagioclase feldspar, pyroxene, and commonly olivine or iron oxides
AI-generated identification · may be incorrectFine-grained, dark brown to black with rusty weathering and a subdued vitreous-to-waxy polish; hardness about 5–6 Mohs, no visible cleavage, dense with specific gravity roughly 2.8–3.0. The rounded shape indicates natural water abrasion or tumbling.
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Physical properties
Fine-grained, dark brown to black with rusty weathering and a subdued vitreous-to-waxy polish; hardness about 5–6 Mohs, no visible cleavage, dense with specific gravity roughly 2.8–3.0. The rounded shape indicates natural water abrasion or tumbling.
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. Its age can range from geologically recent to billions of years; this specimen’s age cannot be determined visually.
Uses & applications
Used as crushed aggregate, road stone, riprap, paving, building stone, and occasionally in landscaping or polished-stone collections; it has little gemstone value.
Geological facts
Rusty brown coloration usually reflects oxidation of iron-bearing minerals, while the dark streaks may be vesicle fillings, weathered inclusions, or finer-grained zones.
Field identification & locations
Identify by its heavy, fine-grained texture, dark color, lack of obvious large crystals, and inability to scratch glass easily; a streak, magnetism test, and thin section would improve certainty. Common in volcanic regions and river gravels worldwide.
