igneous
Dark mafic rock, likely basalt with iron-oxide veining
Basalt; predominantly plagioclase and pyroxene, possibly olivine, with hematite/goethite staining
AI-generated identification · may be incorrectFine-grained, dark gray to black, generally dull to slightly subvitreous, with reddish-brown iron-oxide veins or alteration. Typical basalt hardness is about Mohs 6, with no obvious cleavage and specific gravity around 2.8–3.0; the image alone cannot confirm exact mineralogy.
Identified More igneous →
Explore Dark mafic rock, likely basalt with iron-oxide veining in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine-grained, dark gray to black, generally dull to slightly subvitreous, with reddish-brown iron-oxide veins or alteration. Typical basalt hardness is about Mohs 6, with no obvious cleavage and specific gravity around 2.8–3.0; the image alone cannot confirm exact mineralogy.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and ancient lava flows. Its age may range from recent to billions of years; the reddish material likely reflects later oxidation of iron-bearing minerals or fractures.
Uses & applications
Used as crushed aggregate, road base, riprap, and occasionally dimension stone; attractive polished pieces may be used decoratively. This specimen has modest collector value unless laboratory testing reveals unusual chemistry or a rarer rock type.
Geological facts
The vesicles and irregular fracture visible along parts of the edge are consistent with volcanic basalt, although the specimen appears largely massive and nonvesicular. A streak, density, and thin-section examination would help distinguish basalt from other dark rocks.
Field identification & locations
Common worldwide, especially in Hawaii, Iceland, India’s Deccan Traps, the Columbia River Basalt Group, and oceanic crust. Usually worth about $1–$10 as a loose common specimen, or $10–$30 if unusually attractive or labeled; identification is provisional from the photograph.
