igneous
Vesicular basalt (possibly scoriaceous basalt)
Basalt; chiefly plagioclase feldspar, clinopyroxene, and iron-titanium oxides
AI-generated identification · may be incorrectHardness about 5–6 Mohs; dark gray to black, fine-grained, commonly dull to subtly glassy, with rounded gas vesicles and occasional reddish-brown oxidation staining. Its texture is massive and non-cleavable, with a typical specific gravity near 2.8–3.0.
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Physical properties
Hardness about 5–6 Mohs; dark gray to black, fine-grained, commonly dull to subtly glassy, with rounded gas vesicles and occasional reddish-brown oxidation staining. Its texture is massive and non-cleavable, with a typical specific gravity near 2.8–3.0.
Formation & geological history
An extrusive igneous rock formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; oxidation likely occurred during weathering. Basalt forms from the Precambrian to the present, including recent volcanic flows.
Uses & applications
Used as aggregate, road stone, riprap, paving, and occasionally as a polished decorative or collectible specimen; the pictured rounded piece is likely tumbled or naturally water-worn.
Geological facts
Vesicles distinguish it from most dense basalt, while reddish interiors commonly reflect oxidized iron minerals. It may resemble scoria, but scoria is generally lighter, more porous, and less compact.
Field identification & locations
Identify by its black fine-grained matrix, irregular vesicles, heavy feel, and lack of obvious crystals; common in volcanic regions, river gravels, and oceanic crust. A magnet may show weak attraction from magnetite.
