sedimentary

Conglomerate (possibly breccia)

Polymictic clastic conglomerate; rounded clasts in a dark, likely volcanic-lithic matrix

AI-generated identification · may be incorrect

Dark gray to black, coarse-grained rock containing abundant light-colored rounded to subangular pebbles and grains. Hardness is variable, commonly about 5–7; dull to slightly gritty luster, no consistent cleavage, and specific gravity roughly 2.5–2.8.

Identified September 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when gravel-sized fragments were deposited by energetic rivers, alluvial fans, or shorelines and cemented by silica, carbonate, or iron minerals. Its exact geological age cannot be determined from the photograph.

Uses & applications

Used locally as building or decorative stone and commonly collected as a geological specimen; generally has little jewelry value unless unusually attractive or polished.

Geological facts

The rounded clasts suggest conglomerate, while strongly angular fragments would indicate breccia. The dark matrix may be volcanic rock or iron-rich cement, but laboratory testing is needed for confident identification.

Field identification & locations

Look for pebble-size clasts firmly cemented in a finer matrix; a hand lens, dilute acid test, and examination of clast rounding help distinguish it from breccia or artificial aggregate. Common in ancient river and fan deposits worldwide.