sedimentary

Chert Conglomerate (Potomac Puddle Stone)

Sedimentary Conglomerate with Iron-Oxide matrix

AI-generated identification · may be incorrect

Hardness: 6.5-7 (components); Color: tan, yellow, rust-brown; Luster: dull to waxy; Texture: clastic (rounded pebbles cemented together); Specific Gravity: 2.6-2.7

Hardness: 6
Color: tan, yellow, rust-brown
Luster: dull to waxy

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (components); Color: tan, yellow, rust-brown; Luster: dull to waxy; Texture: clastic (rounded pebbles cemented together); Specific Gravity: 2.6-2.7

Formation & geological history

Formed in high-energy river environments or alluvial fans during the Cretaceous period, where rounded river gravels were cemented by iron-rich minerals over millions of years.

Uses & applications

Used primarily as decorative landscaping stone, drainage material, and as a collector's specimen for local geology enthusiasts.

Geological facts

Commonly nicknamed 'Puddle Stone' in the Mid-Atlantic US, these rocks represent ancient riverbeds that existed over 100 million years ago when dinosaurs roamed the area.

Field identification & locations

Identify by looking for rounded waxy pebbles (chert/quartzite) held together by a gritty, rusty sand or iron matrix. Found frequently in the Potomac River basin and general East Coast coastal plain deposits.