igneous
Weathered volcanic rock, likely altered andesite
Altered andesite; predominantly plagioclase and volcanic pyroxene/amphibole, with secondary iron oxides and clay minerals
AI-generated identification · may be incorrectFine-grained, dull earthy luster, pale green-gray with orange-red oxidation staining and possible vesicles or weathering cavities; estimated Mohs hardness 5–6, no obvious cleavage, and moderate density. Exact identification requires a fresh surface, hand lens, streak, and hardness testing.
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Physical properties
Fine-grained, dull earthy luster, pale green-gray with orange-red oxidation staining and possible vesicles or weathering cavities; estimated Mohs hardness 5–6, no obvious cleavage, and moderate density. Exact identification requires a fresh surface, hand lens, streak, and hardness testing.
Formation & geological history
Likely formed as lava that cooled relatively quickly at or near Earth’s surface, then underwent hydrothermal alteration and weathering. Andesitic volcanism is common in subduction-zone volcanic arcs, with age dependent on its source locality.
Uses & applications
Typically used as local aggregate, road stone, riprap, or landscaping rock; attractive altered pieces may be collected, but this specimen has little commercial value without unusual mineralization.
Geological facts
The green coloration may reflect chlorite or other alteration minerals, while orange-red patches are iron oxides such as hematite or limonite. The rusty cavity could indicate weathered sulfide or iron-rich material.
Field identification & locations
Common in volcanic terrains, especially the Andes, Cascades, Japan, Indonesia, and other island arcs. Look for a fine matrix, scattered tiny crystals, volcanic textures, and reaction to dilute acid (usually none); value is approximately $1–$10 as a common hand specimen, or $10–$30 if locality or mineralization is documented.
