Polygenetic Conglomerate (Puddingstone)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Variegated with red, brown, and tan clasts in a yellowish-green matrix; Luster: Dull to waxy; Texture: Clastic with rounded pebbles; Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the lithification of rounded river or beach gravel transport in a high-energy environment. This specimen appears to be a glacial erratic or river-worn cobble, possibly dating to the Precambrian or Paleozoic eras depending on local geography.

Uses & Applications

Used primarily as decorative stone, lapidary material for cabochons, and historical building stone in specific regions.

Geological Facts

Commonly known as 'Puddingstone' because the dark pebbles resemble raisins or plums in a pudding. In the UK and parts of North America like Michigan and Maryland, specific varieties are highly prized by collectors.

Field Identification & Locations

Identify in the field by looking for rounded, varied 'clasts' (pebbles) firmly cemented in a finer-grained matrix. Often found in glacial till, riverbeds, or sedimentary outcrops. It will not fizz with acid, distinguishing it from limestone-based conglomerates.

Identified on: 5/3/2026

Mode: Standard