sedimentary

Puddingstone

Conglomerate (Jasper Conglomerate)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale); Color: Brownish background with red and black inclusions; Luster: Vitreous to dull; Crystal structure: Clastic/Amorphous; Specific gravity: 2.6-2.7

Hardness: 6
Color: Brownish background with red and black inclusions
Luster: Vitreous to dull

Identified June 19, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Brownish background with red and black inclusions; Luster: Vitreous to dull; Crystal structure: Clastic/Amorphous; Specific gravity: 2.6-2.7

Formation & geological history

Formed approximately 2.3 billion years ago during the Huronian Supergroup. It is a sedimentary rock where fine-grained sand cemented into quartzite, trapping rounded pebbles of red jasper and black chert.

Uses & applications

Used primarily as decorative stones, in lapidary work for jewelry, garden ornaments, and as a popular collector's item. Historically used in masonry.

Geological facts

The St. Joseph Island Puddingstone is world-famous. These rocks were moved southward from Canada into Michigan and Ohio by glacial activity during the last Ice Age.

Field identification & locations

Identified by large, rounded pebbles (clasts) of bright red jasper embedded in a lighter quartzite matrix. Found commonly on beaches in the Great Lakes region, especially Lake Huron.