metamorphic

Rounded quartz-rich metamorphic cobble

Likely quartzite, possibly micaceous quartzite

AI-generated identification · may be incorrect

Hardness about 7 Mohs; pale gray-white with rusty orange-brown iron-oxide staining, granular texture, and dull to slightly vitreous luster. Quartz grains are interlocked with little visible cleavage; reddish streaks may follow fractures or former bedding.

Identified September 18, 2026More metamorphic →

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Physical properties

Formation & geological history

Quartzite forms when quartz-rich sandstone is recrystallized under heat and pressure, commonly during mountain-building; the specimen was later rounded by river or shoreline transport. Its precise geological age cannot be determined from the photograph.

Uses & applications

Used as durable aggregate, landscaping stone, riprap, and occasionally as a decorative or lapidary material. A typical rounded cobble has minimal commercial value.

Geological facts

Quartzite commonly fractures across grains rather than around them and can scratch ordinary glass. Rust-colored patterns generally reflect oxidation of trace iron-bearing minerals, not necessarily jasper.

Field identification & locations

Test with a steel file or glass: genuine quartzite resists scratching; a hand lens should show fused quartz grains. Common in metamorphic mountain belts and gravel deposits worldwide; acid causes no reaction unless carbonate cement is present.