metamorphic
Rounded quartz-rich cobble, likely quartzite or weathered granite
Quartzite (mostly SiO₂), possibly feldspathic quartzite; exact identification requires testing
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; pale gray, tan, pink, and brown with a dull-to-slightly sugary luster, granular texture, and no obvious cleavage. The rounded shape indicates water or glacial abrasion; small pits and iron-oxide staining are visible.
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Physical properties
Hardness about 6.5–7 Mohs; pale gray, tan, pink, and brown with a dull-to-slightly sugary luster, granular texture, and no obvious cleavage. The rounded shape indicates water or glacial abrasion; small pits and iron-oxide staining are visible.
Formation & geological history
If quartzite, it formed when quartz-rich sandstone was metamorphosed under heat and pressure, commonly during Precambrian–Paleozoic mountain building. Its present rounded form likely developed in a river, shoreline, or glacial deposit.
Uses & applications
Common quartzite is used as crushed stone, aggregate, riprap, and occasionally decorative stone; attractive pieces may be polished or collected. It has limited gemstone value unless unusually colorful or patterned.
Geological facts
Quartzite commonly breaks across quartz grains rather than around them and can scratch ordinary glass. The pink and brown colors may reflect feldspar or iron oxides, so the specimen could instead be a strongly weathered granitic or volcanic cobble.
Field identification & locations
Test with a steel knife and glass: genuine quartz-rich material should resist a knife and scratch glass; a vinegar test is uninformative. Inspect a fresh fracture for interlocking quartz grains, and use a streak, density, or thin-section test for confirmation.
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