sedimentary

Chert Pebble (Water-worn Siliceous Pebble)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness 7 on the Mohs scale, smooth rounded shape from stream or glacial erosion, vitreous to waxy luster, greenish-tan to yellowish-brown mottled coloration, lacks cleavage, shell-like (conchoidal) fracture when broken.

Identified July 26, 2026More sedimentary →

Explore Chert Pebble (Water-worn Siliceous Pebble) in the encyclopedia →

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Physical properties

Formation & geological history

Formed through the accumulation and chemical precipitation of microcrystalline silica, often in ancient marine environments. Subsequently eroded, weathered, and rounded by water transport in rivers or glacial till.

Uses & applications

Historically used by Indigenous peoples for flintknapping and tool making due to its predictable conchoidal fracturing. Modern uses include decorative landscaping, gravel aggregate, and hand-held polishers.

Geological facts

Chert and chalcedony pebbles are extremely common in riverbeds and glacial deposits throughout Pennsylvania (near the coordinates 41.6°N, 76.2°W), where Paleozoic sedimentary layers and glacial till are abundant.

Field identification & locations

Identify in the field by its hardness (will easily scratch glass and stainless steel knife blades), smooth stream-rounded texture, and lack of visible grains under magnification.