mineral
Iron-stained quartz-bearing rock
Quartz (SiO₂), likely in a limonite/goethite-rich matrix
AI-generated identification · may be incorrectGray to brown, opaque-to-translucent silica with earthy yellow-brown iron-oxide coatings; vitreous to dull luster, irregular fracture, no obvious cleavage, and Mohs hardness about 7 for quartz (so it can scratch glass).
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Physical properties
Gray to brown, opaque-to-translucent silica with earthy yellow-brown iron-oxide coatings; vitreous to dull luster, irregular fracture, no obvious cleavage, and Mohs hardness about 7 for quartz (so it can scratch glass).
Formation & geological history
Likely formed by hydrothermal or groundwater silica deposition followed by weathering and oxidation of iron-bearing minerals; the exact geological age cannot be determined from the photograph.
Uses & applications
Primarily a collector specimen; quartz-rich material may be used as aggregate or silica source, though this irregular iron-stained piece has little industrial value and is not gem quality.
Geological facts
The brown coloration commonly results from goethite and limonite coatings or inclusions. Metallic-looking patches may be iron oxides rather than native metal.
Field identification & locations
Test a fresh edge for glass-scratching hardness and inspect for quartz’s conchoidal fracture; a streak test may show a yellow-brown to reddish-brown streak from iron oxides. Common in weathered veins, gossans, and hydrothermal districts worldwide.
