sedimentary

Polymict conglomerate (pebble conglomerate)

Clastic sedimentary rock; rounded pebble and granule clasts in a finer-grained matrix

AI-generated identification · may be incorrect

Coarse, poorly sorted rock with rounded reddish and gray clasts in a tan-brown matrix. Clasts likely include quartz-rich and volcanic or other lithic fragments; hardness varies, while quartz-bearing parts are about Mohs 7. No single crystal structure or cleavage.

Identified September 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when transported gravel and sand accumulated in a high-energy river, beach, or alluvial-fan setting, then compacted and cemented. Its age cannot be determined from the image alone.

Uses & applications

Primarily a geological and teaching specimen; conglomerate may be used as dimension stone or aggregate where sufficiently strong and uniform.

Geological facts

Conglomerate is distinguished from breccia by its rounded rather than angular coarse clasts.

Field identification & locations

Look for pebble-sized, rounded fragments firmly enclosed in a finer matrix; the varied clasts indicate mixed source rocks and transport. Conglomerates occur worldwide in ancient river and coastal deposits.