igneous
Likely basalt or basaltic volcanic rock
Fine-grained mafic rock, chiefly plagioclase and clinopyroxene with possible olivine and iron-titanium oxides
AI-generated identification · may be incorrectDark gray to black, dull-to-subvitreous luster, very fine-grained and massive; typically Mohs 6, with no visible cleavage and specific gravity about 2.8–3.0. The image is limited, so vesicles or glassy surfaces cannot be confirmed.
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Physical properties
Dark gray to black, dull-to-subvitreous luster, very fine-grained and massive; typically Mohs 6, with no visible cleavage and specific gravity about 2.8–3.0. The image is limited, so vesicles or glassy surfaces cannot be confirmed.
Formation & geological history
Forms when basaltic lava cools rapidly at or near Earth’s surface, commonly in the Cenozoic to Recent volcanic record, though basalt occurs throughout geologic time.
Uses & applications
Used as crushed aggregate, road base, railway ballast, dimension stone, and occasionally as a decorative material; generally low collector value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the oceanic crust. Its dark color reflects abundant iron- and magnesium-rich minerals.
Field identification & locations
Identify by its black, dense appearance, fine texture, and lack of obvious layered structure; a streak, magnetism, vesicles, or visible crystals can help distinguish it from obsidian or slag. Common worldwide, especially oceanic islands, volcanic fields, and mid-ocean ridges.
