sedimentary
Puddingstone (Jasper-Conglomerate)
Jasper Conglomerate (SiO2 matrix with Jasper clasts)
Hardness: 6.5-7 on Mohs scale; Color: Cream, tan, or white matrix with red, brown, or black inclusions; Luster: Dull to waxy; Texture: Coarse-grained with rounded clasts; Structure: Massive clastic.
- Hardness
- 6
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Cream, tan, or white matrix with red, brown, or black inclusions; Luster: Dull to waxy; Texture: Coarse-grained with rounded clasts; Structure: Massive clastic.
Formation & geological history
Formed during the Huronian Supergroup period (approx. 2.1-2.4 billion years ago). These are ancient river deposits where sand and gravel were cemented over eons, often involving high-pressure silica-rich fluids.
Uses & applications
Primarily used as a collector's item and for lapidary work (polishing, cabochons). Historically used by indigenous peoples for tools and occasionally in local construction as decorative stone.
Geological facts
The 'Michigan Puddingstone' is a famous variety. It is named because it resembles a traditional boiled fruit pudding with raisins (the Jasper clasts) stuck inside the dough (the quartzite matrix).
Field identification & locations
Identify by looking for distinct, rounded red jasper pebbles embedded firmly in a lighter, grainy quartzite matrix. Commonly found in glacial drift areas, particularly in Michigan, Ontario, and around the Great Lakes.
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