igneous
Tumbled dark stone, likely basalt
Basalt; chiefly plagioclase feldspar, pyroxene, and minor olivine or iron oxides
AI-generated identification · may be incorrectFine-grained, dark gray to black, dull to faintly vitreous luster, typically massive with no visible cleavage; Mohs hardness about 6, specific gravity 2.8–3.0. The smooth shape indicates natural water wear or tumbling.
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Physical properties
Fine-grained, dark gray to black, dull to faintly vitreous luster, typically massive with no visible cleavage; Mohs hardness about 6, specific gravity 2.8–3.0. The smooth shape indicates natural water wear or tumbling.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic regions and oceanic crust. Individual formation ages vary from recent eruptions to billions of years old.
Uses & applications
Used as aggregate, road stone, riprap, paving, and sometimes decorative or metaphysical tumbled stone. Small pieces have modest collecting value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly forms extensive lava flows and ocean-floor crust.
Field identification & locations
Identify it by its uniformly dark, fine-grained appearance, heavy feel, and lack of large crystals; a streak, magnetism test, or close inspection may distinguish it from similar dark stones such as andesite or slate. Common worldwide, especially Hawaii, Iceland, India, and oceanic islands.
