metamorphic
Weathered iron-stained quartzite or sandstone cobble
Quartzite (quartz-rich rock), possibly ferruginous sandstone
AI-generated identification · may be incorrectLikely composed mainly of quartz with iron-oxide coatings and minor feldspar/clay. Mohs hardness about 6.5–7 if quartzite; dull to earthy, tan-brown, massive, with no obvious cleavage and moderate-to-high density.
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Physical properties
Likely composed mainly of quartz with iron-oxide coatings and minor feldspar/clay. Mohs hardness about 6.5–7 if quartzite; dull to earthy, tan-brown, massive, with no obvious cleavage and moderate-to-high density.
Formation & geological history
Probably a naturally rounded river or beach cobble formed by abrasion and weathering. If quartzite, its original sandstone was metamorphosed during a mountain-building event; exact age and origin cannot be determined from the photograph.
Uses & applications
Common quartzite is used as aggregate, road stone, landscaping rock, and occasionally building stone; attractive pieces may be collected but are generally low-value.
Geological facts
The rusty coloration is characteristic of oxidized iron minerals such as hematite or goethite. The rounded shape indicates transport by water, ice, or prolonged surface abrasion.
Field identification & locations
Look for a gritty or sugary quartz texture, translucent grains, and resistance to scratching by a steel knife; quartz-rich material should scratch glass. Common worldwide in river gravels and quartzite-bearing mountain regions; definitive identification requires a fresh break or hardness test.
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