Conglomerate

Physical Properties

Hardness: variable based on matrix (6-7 for quartz clasts); Color: brown, grey, tan; Luster: dull/earthy matrix with glassy clasts; Structure: clastic; Cleavage: none; Specific Gravity: 2.5-2.8

Formation & Geological History

Formed through the lithification of rounded gravel and boulders, typically in high-energy environments like riverbeds, alluvial fans, or beaches. Ages range from Precambrian to Recent.

Uses & Applications

Used primarily as low-grade aggregate for roads and construction fill. Occasionally used as ornamental stone if the clasts are colorful or contain semi-precious minerals.

Geological Facts

Conglomerate is often called "puddingstone" because the dark rounded stones in a light matrix resemble raisins in pudding. It is the sedimentary 'cousin' to Breccia, which has angular fragments.

Field Identification & Locations

Identify by looking for rounded, water-worn pebbles (clasts) larger than 2mm cemented together. Commonly found in ancient river channels and mountain bases. Good indicator of past water flow.

Identified on: 4/25/2026

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