igneous
Weathered iron-rich volcanic rock (probable basalt/andesite)
Altered basaltic to andesitic volcanic rock; composition likely plagioclase, pyroxene, and iron oxides
AI-generated identification · may be incorrectDark reddish-brown, tan, and gray coloration with a fine-grained, massive texture and weathered surface; likely Mohs 5–6, dull to slightly earthy luster, no obvious cleavage, and specific gravity about 2.7–3.1. The rounded form suggests prolonged stream or beach abrasion.
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Physical properties
Dark reddish-brown, tan, and gray coloration with a fine-grained, massive texture and weathered surface; likely Mohs 5–6, dull to slightly earthy luster, no obvious cleavage, and specific gravity about 2.7–3.1. The rounded form suggests prolonged stream or beach abrasion.
Formation & geological history
Likely formed as lava that cooled rapidly at or near Earth’s surface, then oxidized and weathered; exact geological age and locality cannot be determined from the photograph. Iron-bearing minerals have produced the red-brown staining.
Uses & applications
Common basalt and andesite are used as aggregate, road stone, riprap, and building stone; attractive polished pieces may be sold as lapidary or teaching specimens, though this example appears ordinary.
Geological facts
The red coloration commonly reflects hematite or other iron-oxide coatings rather than a separate red mineral. The specimen may also be a weathered volcanic cobble rather than a single identifiable mineral.
Field identification & locations
Look for a hard, fine-grained matrix, absence of visible large crystals, and red oxidation surfaces; a streak, density, magnetism, and fresh broken surface would improve identification. Common worldwide in volcanic regions and river gravels.
