igneous
Weathered iron-rich basalt or volcanic rock
Fine-grained mafic rock, likely basalt with iron-oxide weathering (hematite/goethite)
AI-generated identification · may be incorrectDark gray, dull to slightly earthy, with yellow-orange iron-oxide coating and alteration; likely hardness about 5–6, with no obvious cleavage. The granular texture may reflect fine basaltic groundmass, though the image is insufficient for precise mineral identification.
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Physical properties
Dark gray, dull to slightly earthy, with yellow-orange iron-oxide coating and alteration; likely hardness about 5–6, with no obvious cleavage. The granular texture may reflect fine basaltic groundmass, though the image is insufficient for precise mineral identification.
Formation & geological history
Likely formed from rapidly cooled mafic lava, then chemically weathered by oxygen- and water-rich conditions; age cannot be determined from the photograph. Iron oxides commonly develop on exposed basalt and other ferromagnesian rocks.
Uses & applications
Basalt is used as aggregate, roadstone, riprap, and occasionally dimension stone; this weathered specimen has mainly educational or collecting value.
Geological facts
Yellow-orange coloration commonly indicates goethite or limonite, while black or reddish-brown areas may contain magnetite or hematite. A magnet test, streak test, and fresh broken surface would greatly improve identification.
Field identification & locations
Common in volcanic regions and formerly glaciated areas where basaltic cobbles are transported. Test for weak magnetism, a gray-to-brown streak, and lack of fizz with dilute hydrochloric acid; avoid relying on surface color alone.
