sedimentary

Puddingstone (specifically Michigan/Gowganda Puddingstone)

Quartzite Conglomerate (Gowganda Formation)

Hardness: 6.5-7 (composed largely of quartz); Color: Creamy white or light gray matrix with bright red, brown, and black jasper clasts; Luster: Dull to vitreous; Crystal Structure: Clastic; Specific Gravity: Approx 2.6-2.7

Hardness: 6
Luster: Dull to vitreous

Identified May 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed roughly 2.3 billion years ago during the Huronian Supergroup. It began as river-washed pebbles and sand that were deposited in deltaic environments, eventually lithified and metamorphosed into a hard quartzite conglomerate.

Uses & applications

Primarily used for decorative landscaping, lapidary work (jewelry and polished spheres), and as an architectural accent. It is highly prized by rockhounds and collectors.

Geological facts

The name comes from its resemblance to a traditional English plum pudding. It is often found as glacial erratics throughout the Great Lakes region, having been pushed south from Ontario, Canada by glaciers during the last ice age.

Field identification & locations

Identify it by looking for a hard, white/gray fine-grained matrix embedded with distinct, rounded red jasper pebbles. It is common on beaches of St. Joseph Island and the northern shore of Lake Huron.

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