sedimentary
Conglomerate
Conglomerate (Clastic Sedimentary Rock)
Hardness: 6.5-7 (variable based on clast composition); Color: Gray to olive-green matrix with dark rounded clasts; Luster: Dull/Earthy; Structure: Clastic, containing rounded pebbles over 2mm; Cleavage: None
- Hardness
- 6
- Color
- Gray to olive-green matrix with dark rounded clasts
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6.5-7 (variable based on clast composition); Color: Gray to olive-green matrix with dark rounded clasts; Luster: Dull/Earthy; Structure: Clastic, containing rounded pebbles over 2mm; Cleavage: None
Formation & geological history
Formed in high-energy environments like riverbeds or alluvial fans where water current is strong enough to transport large pebbles. The rounding occurs through abrasion over thousands of years before being cemented by minerals like silica or calcite.
Uses & applications
Used primarily as coarse aggregate in construction, road base, and occasionally as decorative stone or landscaping material if the clasts are colorful.
Geological facts
Conglomerate is often called 'puddingstone' because the dark clasts in a lighter matrix resemble raisins in a pudding. It differs from Breccia, which contains sharp, angular fragments.
Field identification & locations
Identify by looking for rounded pebbles (clasts) that are visibly cemented into a finer-grained matrix. It is commonly found in ancient river systems or glacial till. Collectors look for 'Gowganda' or high-contrast varieties.
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