sedimentary
Puddingstone (specifically Michigan/Gowganda Puddingstone)
Conglomerate (Jasper Conglomerate)
Hardness: 6.5–7 (Mohs scale); Color: Cream/white matrix with red, brown, and black inclusions; Luster: Dull to vitreous; Crystal structure: Amorphous/Microcrystalline; Cleavage: None; Specific Gravity: 2.6–2.7.
- Hardness
- 6
- Color
- Cream/white matrix with red, brown, and black inclusions
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Cream/white matrix with red, brown, and black inclusions; Luster: Dull to vitreous; Crystal structure: Amorphous/Microcrystalline; Cleavage: None; Specific Gravity: 2.6–2.7.
Formation & geological history
Formed roughly 2.3 billion years ago during the Huronian Supergroup period. It is a lithified river deposit consisting of rounded jasper and quartz pebbles cemented in a fine-grained quartzite matrix, often transported by glacial movement during the last Ice Age.
Uses & applications
Used primarily for decorative lapidary work, jewelry (cabochons), lawn ornamentation, and as a popular collector's item for rockhounds.
Geological facts
This specific variety is often called the 'St. Joseph Island Puddingstone.' The name 'puddingstone' comes from early English settlers who thought the rock looked like boiled plum pudding with raisins and nuts.
Field identification & locations
Identify by looking for distinct, rounded red jasper 'raisins' embedded in a lighter, sand-like cement. It is commonly found on the beaches of Lake Huron, St. Joseph Island, and throughout the Michigan/Ontario Great Lakes region. Collectors should look for high contrast between the pebbles and matrix.
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