igneous
Dark igneous rock, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; commonly plagioclase ± pyroxene, with possible iron-oxide staining
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to weakly vitreous luster, massive texture, and no obvious cleavage; estimated Mohs hardness 5–6. The rusty orange-brown areas are likely weathering products or iron-oxide coatings.
Identified More igneous →
Explore Dark igneous rock, likely basalt or andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to black, fine-grained, dull to weakly vitreous luster, massive texture, and no obvious cleavage; estimated Mohs hardness 5–6. The rusty orange-brown areas are likely weathering products or iron-oxide coatings.
Formation & geological history
Formed when lava cooled relatively rapidly at or near Earth’s surface, generally during the Cenozoic or older volcanic episodes; exact age cannot be determined visually.
Uses & applications
Common basalt is used as crushed aggregate, road base, riprap, and construction stone; attractive dense pieces may be collected or used decoratively, but this specimen has no gem-quality appearance.
Geological facts
Basalt is the most abundant volcanic rock in oceanic crust, while andesite is common in volcanic arcs. A definitive identification requires a fresh surface, hand-lens examination, and ideally thin-section or chemical analysis.
Field identification & locations
Likely basalt if it is uniformly very dark and dense; lighter gray, porphyritic material would favor andesite. Common localities include volcanic regions worldwide; test for lack of fizz with dilute acid and inspect for tiny crystals or vesicles.
