sedimentary
Puddingstone (specifically Gowganda Tillite or St. Joseph Island Puddingstone)
Jasper Conglomerate
Hardness: 6.5-7 (Mohs scale); Color: White to grey matrix with red jasper and black chert clasts; Luster: Dull to vitreous; Structure: Clastic, poorly sorted; Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- White to grey matrix with red jasper and black chert clasts
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: White to grey matrix with red jasper and black chert clasts; Luster: Dull to vitreous; Structure: Clastic, poorly sorted; Specific Gravity: 2.6-2.7
Formation & geological history
Formed roughly 2.3 billion years ago during the Huronian Supergroup glaciation. It is a lithified glacial till (tillite) where rounded pebbles of jasper and quartz were trapped in a fine-grained sandy matrix.
Uses & applications
Used in ornamental stone carving, lapidary work (jewelry making), decorative landscaping, and historically for sharpening tools.
Geological facts
Many of these specimens are glacial erratics, transported hundreds of miles from their original formation site in the Northern Great Lakes region by glaciers during the last ice age.
Field identification & locations
Identify by looking for the 'fruitcake' appearance of rounded red jasper pebbles embedded in a lighter quartzite or sandstone base. Commonly found in Michigan and Ontario.
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Sandstone or Siltstone
Arenite (if sandstone)
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
Argillaceous sedimentary rock
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Sandstone
Arenite (primarily SiO2)
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