sedimentary
Puddingstone
Polymictic Conglomerate
Hardness (Mohs scale): 6.5-7 (due to silica cementation); Color: Dark brown to red rounded clasts in a light grey or cream matrix; Luster: Dull to waxy; Structure: Clastic with rounded pebbles; Cleavage: None.
- Luster
- Dull to waxy
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Physical properties
Hardness (Mohs scale): 6.5-7 (due to silica cementation); Color: Dark brown to red rounded clasts in a light grey or cream matrix; Luster: Dull to waxy; Structure: Clastic with rounded pebbles; Cleavage: None.
Formation & geological history
Formed through high-energy water transport (rivers or glaciers) that smooths large pebbles, which are then deposited and fused together by a fine-grained silica cement during the lithification process. Common in the Paleozoic and Proterozoic eras.
Uses & applications
Primary use as ornamental stone for landscaping and masonry; historically used for millstones; highly valued by rockhounds and lapidary artists for jewelry and cabochons.
Geological facts
Hertfordshire Puddingstone was historically believed to be a 'lucky stone' that could ward off evil spirits. Its name comes from its resemblance to a traditional Christmas plum pudding with raisins.
Field identification & locations
Identify by looking for distinct, rounded 'pebbles' of one color tightly encased in a solid, lighter 'batter-like' matrix. Commonly found in the UK (Hertfordshire), Canada (St. Joseph Island), and the US (Michigan and Maryland).
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