sedimentary
Puddingstone
Conglomerate (typically quartz-rich or jasper-rich)
Mohs hardness: 6.5-7.0 (mostly silica-based); Color: Cream or tan matrix with red and brown clasts; Luster: Dull to vitreous; Crystal structure: Amorphous/microcrystalline matrix; Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Cream or tan matrix with red and brown clasts
- Luster
- Dull to vitreous
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Physical properties
Mohs hardness: 6.5-7.0 (mostly silica-based); Color: Cream or tan matrix with red and brown clasts; Luster: Dull to vitreous; Crystal structure: Amorphous/microcrystalline matrix; Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed in ancient riverbeds or coastal environments during the Paleoproterozoic era (approx. 2.3 billion years ago). Rounded pebbles (clasts) were deposited in a sandy matrix and later lithified through heat and pressure.
Uses & applications
Primarily used as a decorative stone in jewelry (cabochons), paperweights, and ornamental garden stones. Historically used for building materials and grinding stones in some regions.
Geological facts
The most famous variety is the 'Hertfordshire Puddingstone' from England and the 'St. Joseph Island Puddingstone' from the Great Lakes region. It gets its name because the dark pebbles in the light matrix resemble raisins in a plum pudding.
Field identification & locations
Identify in the field by looking for rounded, varied-color pebbles embedded in a finer, cement-like matrix. Commonly found in glacier-displaced areas like the Great Lakes region or southern England. Collectors look for high contrast and intact pebbles.
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