sedimentary
Puddingstone (Jasper-Conglomerate)
Conglomerate (Silicon Dioxide, SiO2 with impurities)
Hardness: 6.5-7 Mohs. Color: White or cream quartz matrix with red, brown, or black jasper inclusions. Luster: Dull to waxy. Structure: Clastic/Granular. Cleavage: None.
- Hardness
- 6
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 Mohs. Color: White or cream quartz matrix with red, brown, or black jasper inclusions. Luster: Dull to waxy. Structure: Clastic/Granular. Cleavage: None.
Formation & geological history
Formed roughly 2.3 billion years ago during the Huronian Supergroup era. It consists of rounded pebbles of jasper and quartz cemented together by a fine-grained quartz sand matrix under intense heat and pressure.
Uses & applications
Commonly used for lapidary work, jewelry, garden decoration, and as a popular collector's item in the Great Lakes region.
Geological facts
The most famous variety is the St. Joseph Island Puddingstone. It is often referred to as a 'conglomerate' because it is a mixture of different minerals and rocks fused together like a fruit pudding.
Field identification & locations
Identify by the distinct 'red spots' (jasper) embedded in a lighter quartzite matrix. Frequently found on the beaches of Lake Huron and throughout Michigan and Ontario.
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