sedimentary
Conglomerate
Conglomerate (SiO2 dominant in clasts)
Hardness: 6.5-7 (for quartz clasts); Color: Variable browns, tans, and whites; Luster: Dull matrix with vitreous clasts; Crystal structure: Amorphous/microcrystalline; Cleavage: None; SG: 2.6-2.7
- Hardness
- 6
- Color
- Variable browns, tans, and whites
- Luster
- Dull matrix with vitreous clasts
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Physical properties
Hardness: 6.5-7 (for quartz clasts); Color: Variable browns, tans, and whites; Luster: Dull matrix with vitreous clasts; Crystal structure: Amorphous/microcrystalline; Cleavage: None; SG: 2.6-2.7
Formation & geological history
Formed through the lithification of rounded gravel and pebbles, typically in high-energy environments like riverbeds, beaches, or alluvial fans where water current rounds the stones.
Uses & applications
Used primarily as coarse aggregate in the construction industry for concrete and road beds; occasionally used as decorative stone or for geological education.
Geological facts
Conglomerate is often called 'puddingstone' because the rounded pebbles look like raisins or nuts in a pudding. It serves as a historical record of ancient water flow speeds.
Field identification & locations
Identify by looking for rounded, smooth pebbles (clasts) larger than 2mm cemented together by a finer-grained matrix. Commonly found in sedimentary basins and ancient river deposits.
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