metamorphic

Polished brown river pebble, likely quartzite

Quartzite (mostly microcrystalline SiO₂), identification tentative from appearance

AI-generated identification · may be incorrect

Hardness about 7 Mohs; brown, tan, and gray mottling with a polished vitreous-to-waxy luster. Dense, massive, fine-grained, and lacking visible cleavage; likely specific gravity around 2.6–2.7.

Identified September 9, 2026More metamorphic →

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Physical properties

Hardness about 7 Mohs; brown, tan, and gray mottling with a polished vitreous-to-waxy luster. Dense, massive, fine-grained, and lacking visible cleavage; likely specific gravity around 2.6–2.7.

Formation & geological history

Formed when quartz-rich sandstone recrystallized under heat and pressure, commonly during mountain-building; exact geological age cannot be determined from the image. Its rounded shape indicates later river or beach abrasion, followed by human polishing.

Uses & applications

Used as crushed stone, aggregate, paving, architectural stone, and occasionally decorative or lapidary material. This small polished specimen has modest collectible value.

Geological facts

Quartzite commonly resembles quartz-rich sandstone but is harder and more tightly interlocked; individual grains may sparkle under magnification.

Field identification & locations

Field tests include a scratch test against glass, which it should scratch, and resistance to steel; it typically lacks acid reaction and splits irregularly rather than along bedding. Common worldwide in metamorphic mountain belts and river gravels.