sedimentary
Conglomerate
Conglomerate (Sedimentary Clastic Rock)
Hardness: 6.5-7 (variable based on clasts); Color: earthy grays, browns, and tans; Luster: dull to earthy; Crystal structure: clastic (granular); Cleavage: none; Specific gravity: 2.6-2.8
- Hardness
- 6
- Color
- earthy grays, browns, and tans
- Luster
- dull to earthy
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Physical properties
Hardness: 6.5-7 (variable based on clasts); Color: earthy grays, browns, and tans; Luster: dull to earthy; Crystal structure: clastic (granular); Cleavage: none; Specific gravity: 2.6-2.8
Formation & geological history
Formed through the lithification of rounded gravel and boulder-sized clasts. Usually found in high-energy environments like riverbeds or alluvial fans where water currents are strong enough to move heavy stones and round them through abrasion.
Uses & applications
Used primarily as coarse aggregate for concrete and road construction. Smaller, more colorful versions can be used as decorative building stone or 'puddingstone' for collectors.
Geological facts
Conglomerate is often called a 'natural concrete.' Famous specimens include the 'Puddingstones' from Hertfordshire and Michigan. Martian conglomerate discovered by the Curiosity rover proved that liquid water once flowed on Mars.
Field identification & locations
Identify it by its 'chunky' appearance, specifically the presence of rounded pebbles cemented together by a finer-grained matrix. Commonly found in old river drainage basins or coastal areas.
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