sedimentary
Jasper Conglomerate (specifically Puddingstone)
Jasper Conglomerate (Siliceous sedimentary rock)
Hardness: 6.5-7 (Mohs scale); Color: Cream or white matrix with reddish-brown or purple jasper clasts; Luster: Dull to waxy; Structure: Clastic; Specific Gravity: 2.6-2.7
- Hardness
- 6
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Cream or white matrix with reddish-brown or purple jasper clasts; Luster: Dull to waxy; Structure: Clastic; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the lithification of rounded river or beach pebbles of jasper and quartz cemented by a fine-grained silica matrix. Common in Precambrian formations (approx. 2.3 billion years old), particularly the Lorrain Formation of the Huronian Supergroup.
Uses & applications
Primarily used as an ornamental stone, for lapidary work (cabochons and polished specimens), and historically used for grinding stones or millstones due to its extreme hardness.
Geological facts
Also known as 'St. Joseph Island Puddingstone' in the Great Lakes region. The name 'Puddingstone' comes from its resemblance to a traditional English plum pudding which contains raisins and nuts inside a doughy matrix.
Field identification & locations
Identify in the field by looking for rounded, colorful 'blobs' of jasper (usually red) firmly embedded in a harder, lighter-colored quartzite or silica matrix. Frequently found in the glacial drift of Michigan, Ontario, and around the Great Lakes.
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