sedimentary
Conglomerate
Conglomerate (Detrital sedimentary rock)
Hardness: variable (depends on clast type, usually 6-7 if quartz-rich); Color: earthy grays, browns, and reds; Luster: dull to earthy; Structure: clastic texture with rounded gravel-sized fragments (>2mm) in a finer matrix; Cleavage: none; Specific Gravity: 2.6-2.8.
- Hardness
- variable (depends on clast type, usually 6-7 if quartz-rich)
- Color
- earthy grays, browns, and reds
- Luster
- dull to earthy
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Physical properties
Hardness: variable (depends on clast type, usually 6-7 if quartz-rich); Color: earthy grays, browns, and reds; Luster: dull to earthy; Structure: clastic texture with rounded gravel-sized fragments (>2mm) in a finer matrix; Cleavage: none; Specific Gravity: 2.6-2.8.
Formation & geological history
Formed through the lithification of rounded rocks and pebbles, usually in high-energy environments such as fast-flowing rivers, alluvial fans, or glaciated areas. The rounding indicates significant transport distance from the source rock.
Uses & applications
Used primarily in the construction industry as coarse aggregate for concrete and road-base material. Occasionally used as ornamental stone if the clasts are colorful or unique, such as 'puddingstone'.
Geological facts
Conglomerate is often nicknamed 'Puddingstone' because the rounded pebbles look like raisins or nuts in a cake. It is a key indicator for geologists to locate ancient riverbeds and shorelines.
Field identification & locations
Identify in the field by looking for large, rounded pebbles (clasts) cemented together in a finer-grained sandy or silty matrix. It is commonly found in sedimentary basins and mountain foothills. For collectors, look for specimens with contrasting colors between the pebbles and the cement.
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