sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness: 6.5-7 (based on quartz content); Color: Gray, tan, brown with multi-colored inclusions; Luster: Dull or earthy; Structure: Clastic with rounded clasts; Cleavage: None (breaks across grains)
- Hardness
- 6
- Color
- Gray, tan, brown with multi-colored inclusions
- Luster
- Dull or earthy
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Physical properties
Hardness: 6.5-7 (based on quartz content); Color: Gray, tan, brown with multi-colored inclusions; Luster: Dull or earthy; Structure: Clastic with rounded clasts; Cleavage: None (breaks across grains)
Formation & geological history
Formed through the lithification of rounded gravel and boulder-sized clasts. These are typically deposited in high-energy environments like fast-moving rivers or beaches where water action rounds the stones over millions of years.
Uses & applications
Used in the construction industry as coarse aggregate for concrete and road-base material. Some attractive specimens are polished for use as ornamental stones.
Geological facts
Conglomerate is often called 'puddingstone' because the rounded pebbles look like raisins or nuts in a pudding. It is essentially a natural version of man-made concrete.
Field identification & locations
Identify in the field by looking for rounded pebbles (at least 2mm in size) cemented within a finer-grained matrix. It is common in riverbeds and ancient sedimentary basins worldwide.
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