igneous
Dark river boulder, probably basalt or dolerite
Likely basalt (fine-grained mafic volcanic rock); exact identification is uncertain from the photograph
AI-generated identification · may be incorrectDark gray to black, massive and rounded by water; likely fine-grained with a dull to weakly lustrous surface. Basalt is typically Mohs 6, chiefly plagioclase and pyroxene, sometimes with olivine; grain size and cleavage cannot be confirmed from this image.
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Physical properties
Dark gray to black, massive and rounded by water; likely fine-grained with a dull to weakly lustrous surface. Basalt is typically Mohs 6, chiefly plagioclase and pyroxene, sometimes with olivine; grain size and cleavage cannot be confirmed from this image.
Formation & geological history
If basalt, it formed when mafic lava cooled at or near the surface; dolerite is a similar composition that cooled underground. The boulder’s age cannot be determined visually; river abrasion rounded it during transport.
Uses & applications
Basalt and dolerite are used as road aggregate, paving stone, and construction material; this large boulder is mainly a natural landscape feature.
Geological facts
A smooth, water-worn shape does not identify the rock by itself; fresh broken surfaces and visible grain size are more diagnostic.
Field identification & locations
The reported location in central Ethiopia is geologically compatible with volcanic rocks, but the photo alone cannot distinguish basalt from other dark rocks. Look for a fresh surface and tiny crystals; a hand lens and streak/hardness tests can help.
