metamorphic
Rounded gray metamorphic cobble, likely quartzite or gneiss
Quartz-rich metamorphic rock; possibly quartzite (mostly SiO₂) or banded gneiss
AI-generated identification · may be incorrectHardness approximately 6.5–7 for quartzite; gray-blue and whitish, with dull to slightly glassy luster and possible foliation or banding. The rounded shape indicates water or glacial abrasion; exact identification requires a close inspection and hardness/streak tests.
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Physical properties
Hardness approximately 6.5–7 for quartzite; gray-blue and whitish, with dull to slightly glassy luster and possible foliation or banding. The rounded shape indicates water or glacial abrasion; exact identification requires a close inspection and hardness/streak tests.
Formation & geological history
Likely formed when quartz-rich sandstone recrystallized under heat and pressure, or from metamorphosed layered rock if the bands are mineral foliation. Such rocks commonly range from Precambrian to Paleozoic ages, depending on locality.
Uses & applications
Used as durable aggregate, landscaping stone, paving material, and occasionally as a decorative or cabochon stone. This unprepared cobble has little commercial value.
Geological facts
Quartzite is highly resistant to weathering and commonly forms ridges and resistant stream gravels. If it splits into thin planar layers, gneiss or another foliated metamorphic rock is more likely.
Field identification & locations
Look for interlocking quartz grains, very high hardness, and inability to scratch with a steel knife; quartz-rich material commonly scratches glass. Common sources include mountain streams, glacial deposits, and quartzite-bearing regions.
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