Puddingstone (Gowganda Tillite/Jasper Conglomerate)

Physical Properties

Hardness: 6.5-7 (Mohs). Color: Tan/cream matrix with embedded red jasper clasts. Luster: Dull/waxy. Texture: Clastic/Coarse.

Formation & Geological History

Formed roughly 2.3 billion years ago during the Huronian glaciation. It is a lithified glacial till (tillite) where red jasper pebbles were trapped in a fine-grained sandy matrix.

Uses & Applications

Used in ornamental stone carving, lapidary work (jewelry), and historical building material. Frequently collected as a decorative garden or shelf specimen.

Geological Facts

The red clasts are typically jasper, while the creamy matrix is quartz sand. It was famously used to mark the 'original' location of Plymouth Rock by some mistaken historical accounts, and is the state rock of Michigan (unofficially) and common in Ontario.

Field Identification & Locations

Identify by looking for distinct bright red or dark brown rounded pebbles 'frozen' in a lighter, harder matrix that cannot be scratched by a steel knife. Found in Great Lakes glacial drift.

Identified on: 5/15/2026

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