igneous
Weathered iron-rich volcanic rock
Likely altered basalt or andesite with iron-oxide staining
AI-generated identification · may be incorrectDark gray to reddish-brown, fine-grained and massive, with dull to subtly earthy luster; apparent hardness about 5–6 Mohs. Red coloration likely comes from hematite/goethite coatings and weathering, while pale patches may be feldspar, quartz, or surface lichen.
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Physical properties
Dark gray to reddish-brown, fine-grained and massive, with dull to subtly earthy luster; apparent hardness about 5–6 Mohs. Red coloration likely comes from hematite/goethite coatings and weathering, while pale patches may be feldspar, quartz, or surface lichen.
Formation & geological history
Probably a volcanic lava formed when basaltic-to-andesitic magma cooled rapidly at or near Earth’s surface, then underwent oxidation and surface weathering. Exact age and composition cannot be determined from the photograph alone.
Uses & applications
Useful as crushed aggregate, road stone, riprap, or landscaping rock; attractive polished pieces may have minor decorative or teaching value.
Geological facts
Iron oxidation commonly produces red, purple, brown, and orange zones in volcanic rocks. Surface lichens and weathering can obscure the original texture and mineralogy.
Field identification & locations
Common in volcanic terrains worldwide; identify by its dense fine grain, lack of obvious layering, dark color, and red iron staining. A fresh broken surface, streak test, acid test, and hardness test would improve identification.
