igneous
Polished dark stone, likely basalt or gabbro
Basalt (fine-grained mafic rock), possibly gabbro; chiefly plagioclase and pyroxene with iron-magnesium minerals
AI-generated identification · may be incorrectDark gray to black, compact, and subtly speckled with a polished luster; typically hardness about 6, no visible cleavage, and specific gravity around 2.8–3.1. The rounded triangular shape and shine indicate tumbling or polishing.
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Physical properties
Dark gray to black, compact, and subtly speckled with a polished luster; typically hardness about 6, no visible cleavage, and specific gravity around 2.8–3.1. The rounded triangular shape and shine indicate tumbling or polishing.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface; gabbro is its coarse-grained intrusive equivalent. Most specimens formed during relatively recent volcanic episodes, though exact age cannot be determined visually.
Uses & applications
Used as aggregate, paving stone, building stone, and decorative material; small polished pieces are inexpensive collectibles or craft stones rather than gemstones.
Geological facts
Basalt is the most widespread volcanic rock on Earth and forms much of the oceanic crust. Its dark color reflects abundant iron- and magnesium-rich minerals.
Field identification & locations
Identify by its dark color, heavy feel, fine grain, and lack of visible glass or large crystals; a magnet may show weak attraction if magnetite is present. Common worldwide, especially in volcanic regions and river gravels.
