metamorphic

Rounded quartzite cobble

Quartzite; predominantly microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Hardness about 7 Mohs; gray-beige to brown, weathered surface, dull to slightly vitreous luster, very fine-grained interlocking quartz crystals, no obvious cleavage, specific gravity about 2.6–2.7.

Identified September 1, 2026More metamorphic →

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Physical properties

Hardness about 7 Mohs; gray-beige to brown, weathered surface, dull to slightly vitreous luster, very fine-grained interlocking quartz crystals, no obvious cleavage, specific gravity about 2.6–2.7.

Formation & geological history

Formed when quartz-rich sandstone was subjected to heat and pressure, recrystallizing into quartzite; the specimen was later rounded by stream or glacial transport. Its precise geological age cannot be determined from the image.

Uses & applications

Used as durable aggregate, road stone, building and paving stone, and occasionally as a decorative or lapidary material; this ordinary cobble has little commercial value.

Geological facts

Quartzite commonly breaks across grains rather than around them and can scratch glass. Brown coloration likely reflects iron-oxide staining or weathering.

Field identification & locations

Identify it by its very hard, dense texture and lack of visible sand grains or clay layers; a steel knife generally will not scratch it. Common in mountain belts and gravel deposits worldwide.