Puddingstone (specifically Gowganda Tillite or St. Joseph Island Puddingstone)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: White to grey matrix with red jasper and black chert clasts; Luster: Dull to vitreous; Structure: Clastic, poorly sorted; Specific Gravity: 2.6-2.7

Formation & Geological History

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

Uses & Applications

Used in ornamental stone carving, lapidary work (jewelry making), decorative landscaping, and historically for sharpening tools.

Geological Facts

Many of these specimens are glacial erratics, transported hundreds of miles from their original formation site in the Northern Great Lakes region by glaciers during the last ice age.

Field Identification & Locations

Identify by looking for the 'fruitcake' appearance of rounded red jasper pebbles embedded in a lighter quartzite or sandstone base. Commonly found in Michigan and Ontario.

Identified on: 5/18/2026

Mode: Standard