Sedimentary

Puddingstone

Conglomerate

Hardness varies depending on clasts and matrix but generally high (6-7 on Mohs scale due to quartz/chert), clasts of strongly contrasting colors (often red jasper, chert, quartzite) set in a lighter matrix (usually quartz sand or quartzite). Luster is dull to vitreous where cut/polished.

Identified May 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy sedimentary environments like fast-moving rivers or beaches where pebbles are deposited into sand, followed by lithification over millions of years. Glacial transport often deposits these as rounded erratics.

Uses & applications

Commonly used for landscaping, as decorative stones, in lapidary for bookends and cabochons, and prized by collectors.

Geological facts

The name 'puddingstone' comes from its resemblance to a traditional plum pudding, with the dark pebbles acting as the 'plums'. Famous varieties include the Roxbury Puddingstone in Massachusetts and the Drummond Island Puddingstone in Michigan.

Field identification & locations

Identifiable by its distinct rounded to sub-angular pebbles of contrasting colors (especially red jasper) tightly bound in a lighter, often quartz-rich matrix. Extremely common around the Great Lakes region as glacial erratics.