igneous
Iron-rich basaltic concretion or weathered basalt
Basalt, predominantly plagioclase and pyroxene with iron-oxide alteration
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to slightly earthy luster, with rusty red-brown iron-oxide staining; typically hardness 5–6 Mohs, no visible cleavage, and high density. The rounded shape and surface texture suggest wave-worn basalt or an iron-rich concretion.
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Physical properties
Dark gray-brown, fine-grained, dull to slightly earthy luster, with rusty red-brown iron-oxide staining; typically hardness 5–6 Mohs, no visible cleavage, and high density. The rounded shape and surface texture suggest wave-worn basalt or an iron-rich concretion.
Formation & geological history
Likely formed as volcanic basalt that cooled rapidly at or near Earth’s surface, later weathering and becoming rounded by coastal transport; basalt ranges from Precambrian to modern age. Exact identification and age require a fresh surface or laboratory testing.
Uses & applications
Common basalt is used as aggregate, riprap, road material, and building stone; this individual specimen has little commercial value but may interest collectors.
Geological facts
Basalt commonly contains tiny plagioclase and pyroxene crystals that are difficult to see without magnification. Rust-colored areas reflect oxidation of iron-bearing minerals.
Field identification & locations
Common in volcanic regions and beaches near basaltic bedrock, including Iceland, Hawaii, Japan, and parts of the Pacific Northwest. Check for a very fine texture, heavy weight, weak or absent acid reaction, and possible attraction to a magnet from iron minerals.
