igneous
Likely basalt (dark volcanic rock)
Basalt; fine-grained mafic volcanic rock, mainly plagioclase and pyroxene, commonly with olivine
AI-generated identification · may be incorrectDark gray to black, fine-grained, with a dull to slightly glassy wet surface; Mohs hardness about 6. It appears massive, but the image does not reveal diagnostic crystals or cleavage.
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Physical properties
Dark gray to black, fine-grained, with a dull to slightly glassy wet surface; Mohs hardness about 6. It appears massive, but the image does not reveal diagnostic crystals or cleavage.
Formation & geological history
Forms when iron- and magnesium-rich lava cools quickly at or near the surface. Basalt occurs from geologically recent eruptions to rocks billions of years old; this specimen’s age and exact identity cannot be determined from the photo.
Uses & applications
Used as crushed aggregate, road stone, and building material; attractive pieces may be kept as geological specimens.
Geological facts
Basalt is among Earth’s most abundant volcanic rocks and forms much of the ocean floor.
Field identification & locations
The dark color and dense, fine-grained appearance are consistent with basalt, but the specimen could be another dark rock; a fresh surface and close inspection for grains or vesicles would help confirm it. Common worldwide, especially in volcanic regions and oceanic crust.
