igneous
Weathered basalt or iron-rich volcanic rock
Mafic volcanic rock, likely basalt; exact identification requires testing
AI-generated identification · may be incorrectDark brown to gray, dull earthy luster, fine-grained and irregularly fractured, with possible vesicles or weathered inclusions. Typical basalt hardness is about 6 Mohs and specific gravity 2.8–3.1; cleavage is absent.
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Physical properties
Dark brown to gray, dull earthy luster, fine-grained and irregularly fractured, with possible vesicles or weathered inclusions. Typical basalt hardness is about 6 Mohs and specific gravity 2.8–3.1; cleavage is absent.
Formation & geological history
Likely formed from rapidly cooled mafic lava, commonly during the Cenozoic or older volcanic episodes, then altered by oxidation and surface weathering. The rusty-brown color may reflect iron-bearing minerals transforming to hematite or limonite.
Uses & applications
Basalt is used as crushed aggregate, road stone, concrete material, and occasionally dimension stone; this weathered fragment has little commercial or jewelry value.
Geological facts
Basalt commonly contains plagioclase, pyroxene, and sometimes olivine or magnetite. Its dark color and possible magnetism distinguish it from many sedimentary rocks.
Field identification & locations
Look for a dense fine-grained texture, no visible sedimentary layers, and weak-to-strong attraction to a magnet if magnetite is present. A fresh broken surface, streak, hardness, and thin-section examination would be needed for certainty; common worldwide in volcanic regions.
