Sedimentary
Conglomerate
Conglomerate (Clastic Sedimentary Rock)
Hardness: 2-7 (variable based on matrix and clasts); Color: Variable brown, grey, rust; Luster: Dull/Earthy; Structure: Clastic with rounded clasts larger than 2mm diamater; Specific Gravity: 2.1-2.9.
- Hardness
- 2-7 (variable based on matrix and clasts)
- Color
- Variable brown, grey, rust
- Luster
- Dull/Earthy
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Physical properties
Hardness: 2-7 (variable based on matrix and clasts); Color: Variable brown, grey, rust; Luster: Dull/Earthy; Structure: Clastic with rounded clasts larger than 2mm diamater; Specific Gravity: 2.1-2.9.
Formation & geological history
Formed through the lithification of rounded gravel and boulders. Usually found in high-energy environments like riverbeds, alluvial fans, or glacial washouts where water movement is fast enough to round stone edges.
Uses & applications
Used primarily as coarse aggregate in construction, road fill, and occasionally as a decorative facing stone in architecture. Minor value for lapidary work if the clasts are colorful minerals like jasper.
Geological facts
Conglomerate is often called 'puddingstone' because it resembles fruit in a pudding. It is the sedimentary 'cousin' of Breccia, which contains angular rather than rounded fragments.
Field identification & locations
Identify in the field by looking for rounded, smooth pebbles or cobbles cemented together in a finer-grained matrix. Found globally in ancient river systems and mountain basins.
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