sedimentary
Jasper Conglomerate (Puddingstone)
Jasper Conglomerate (SiO2 matrix with quartz/jasper clasts)
Hardness: 6.5–7 on Mohs scale; Color: Red, brown, and tannish-white; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.
- Hardness
- 6
- Color
- Red, brown, and tannish-white
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Red, brown, and tannish-white; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.
Formation & geological history
Formed through the lithification of water-worn pebbles (clasts) cemented together by a fine-grained silica-rich matrix. These are typically Proterozoic in age, formed in ancient high-energy riverbeds or coastal environments.
Uses & applications
Used primarily for decorative purposes, lapidary work (cabochons), as garden ornaments, and as a popular collector's item due to its unique 'fruit cake' appearance.
Geological facts
Famous varieties include the Hertfordshire Puddingstone in the UK and the Saint Joseph Island Puddingstone in the Great Lakes region. In folk magic, they were once believed to ward off evil.
Field identification & locations
Identify by the presence of rounded, multicolored pebbles (usually red jasper or white quartz) encased in a very hard, fine-grained matrix. Found commonly on beaches and in glacial till in the Great Lakes region or the UK.
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