igneous
Weathered basalt or iron-rich volcanic rock
Fine-grained mafic igneous rock, likely basalt; exact identification requires testing
AI-generated identification · may be incorrectDark reddish-brown, dull to weakly earthy luster, fine-grained and apparently massive, with no visible crystals or cleavage. Basalt typically has Mohs hardness 5–6 and specific gravity about 2.8–3.0; the red color likely reflects iron-oxide weathering.
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Physical properties
Dark reddish-brown, dull to weakly earthy luster, fine-grained and apparently massive, with no visible crystals or cleavage. Basalt typically has Mohs hardness 5–6 and specific gravity about 2.8–3.0; the red color likely reflects iron-oxide weathering.
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly during volcanic eruptions; its age may range from recent to billions of years. Surface oxidation and weathering can produce the brown-red coating.
Uses & applications
Used as crushed aggregate, road stone, railroad ballast, riprap, and occasionally decorative stone; this small weathered fragment has little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms lava flows, dikes, and ocean-floor pillow lavas.
Field identification & locations
Identify it by its heavy feel, fine texture, lack of obvious quartz, and inability to scratch with a copper coin; a steel file should barely scratch it. Common worldwide, especially volcanic terrains; magnetism may indicate abundant iron-bearing minerals.
