metamorphic
Iron-stained quartz/quartzite pebble
Quartz (SiO₂), likely quartzite or quartz-rich vein rock with iron oxides
AI-generated identification · may be incorrectGray to reddish-brown, massive and granular, with a dull to weakly glassy luster. Quartz hardness is about 7 Mohs; no obvious cleavage, uneven fracture, and typically high specific gravity only where iron oxides are abundant.
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Physical properties
Gray to reddish-brown, massive and granular, with a dull to weakly glassy luster. Quartz hardness is about 7 Mohs; no obvious cleavage, uneven fracture, and typically high specific gravity only where iron oxides are abundant.
Formation & geological history
Likely formed from quartz-rich material, either metamorphosed sandstone (quartzite) or a hydrothermal quartz vein, later weathered and rounded. Iron-bearing fluids produced the reddish-brown hematite/goethite staining; age cannot be determined from the photograph.
Uses & applications
Common specimens have little commercial value, though quartzite is used as aggregate, road stone, and building stone. Attractive iron-stained pieces may be collected or polished.
Geological facts
Quartz should scratch ordinary glass, while a steel knife generally does not scratch it. The rusty coloration is commonly caused by hematite or limonite rather than the main rock itself.
Field identification & locations
The rounded form suggests an alluvial pebble. Check for abundant interlocking quartz grains, glass-scratching hardness, and lack of fizz with dilute acid. Quartz-rich rocks and iron-stained gravels are plausible near 24.8°N, 107.4°W in Sinaloa, Mexico, but the exact locality cannot be confirmed visually.
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