igneous
Weathered iron-rich volcanic rock (probable basalt or andesite)
Altered basalt/andesite, composed chiefly of plagioclase, pyroxene, and iron oxides/hydroxides
AI-generated identification · may be incorrectHardness about 5–6, reddish-brown to gray, dull to earthy luster, fine-grained and massive; the rusty color likely reflects hematite/goethite weathering, with possible pale silica or feldspar veins. Crystal structure is mostly microscopic, with no obvious cleavage.
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Physical properties
Hardness about 5–6, reddish-brown to gray, dull to earthy luster, fine-grained and massive; the rusty color likely reflects hematite/goethite weathering, with possible pale silica or feldspar veins. Crystal structure is mostly microscopic, with no obvious cleavage.
Formation & geological history
Likely an extrusive volcanic rock formed when lava cooled rapidly, then chemically weathered and oxidized near Earth’s surface. Its exact geological age cannot be determined from the photograph.
Uses & applications
Common volcanic rock is used as aggregate, road material, riprap, and landscaping stone; this specimen has modest value as a hand specimen unless locality or unusual mineralization is documented.
Geological facts
Iron oxidation commonly produces red, orange, and brown surfaces and can obscure the original basaltic or andesitic texture.
Field identification & locations
Look for a dense fine-grained texture, very small crystals, rusty iron staining, and weak attraction to a magnet if magnetite is present; a streak, hardness, and acid test would improve identification. Similar rocks occur worldwide in volcanic terrains.
