igneous
Veined basalt or dark mafic metamorphic rock
Basalt, likely altered and quartz/calcite-veined; exact identification requires testing
AI-generated identification · may be incorrectFine- to medium-grained, dark gray-black, with pale yellowish mineral veins and a weathered/tumbled surface. Basalt typically has Mohs hardness 5–6, dull to faintly vitreous luster, interlocking crystals, and no prominent cleavage; veins may fizz with dilute acid if calcite.
Identified More igneous →
Explore Veined basalt or dark mafic metamorphic rock in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine- to medium-grained, dark gray-black, with pale yellowish mineral veins and a weathered/tumbled surface. Basalt typically has Mohs hardness 5–6, dull to faintly vitreous luster, interlocking crystals, and no prominent cleavage; veins may fizz with dilute acid if calcite.
Formation & geological history
Basalt forms from rapidly cooled mafic lava, commonly in oceanic crust and volcanic provinces; the veins formed later when mineral-rich fluids filled fractures. Basaltic rocks range from Precambrian to modern age, and this specimen’s age cannot be determined visually.
Uses & applications
Used as aggregate, roadstone, riprap, paving, and occasionally as a decorative or lapidary stone; this rounded specimen is primarily collectible.
Geological facts
The dark matrix likely contains plagioclase and pyroxene, with possible olivine or opaque iron-titanium minerals. Pale veins may consist of calcite, quartz, zeolite, or epidote, requiring hardness and acid tests for confirmation.
Field identification & locations
Common in volcanic regions, ocean beaches, and glacial deposits; look for dark fine grain, heavy weight, and vesicles or mineral-filled fractures. A steel file should scratch some weathered surfaces, while quartz veins resist scratching.
