sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness varies by cement (usually 6-7 if siliceous); Color: grey matrix with light-colored rounded clasts; Luster: dull; Structure: clastic texture with rounded gravel-sized grains; Specific gravity: 2.6-2.8.
- Color
- grey matrix with light-colored rounded clasts
- Luster
- dull
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Physical properties
Hardness varies by cement (usually 6-7 if siliceous); Color: grey matrix with light-colored rounded clasts; Luster: dull; Structure: clastic texture with rounded gravel-sized grains; Specific gravity: 2.6-2.8.
Formation & geological history
Formed through the lithification of rounded water-worn pebbles and cobbles, typically in high-energy environments like riverbeds, alluvial fans, or beaches. These sediments are deposited and then cemented together over millions of years by minerals like quartz or calcite.
Uses & applications
Used in the construction industry as a decorative stone, aggregate for concrete, and occasionally as a building stone. In the energy industry, it can serve as a reservoir rock for petroleum and natural gas.
Geological facts
Conglomerate is often nicknamed 'puddingstone' because the rounded clasts resemble raisins or nuts in a pudding. It is notably distinct from breccia, which contains angular fragments rather than rounded ones.
Field identification & locations
Identify in the field by looking for rounded pebbles (clasts) larger than 2mm embedded in a finer-grained matrix. It is common in ancient river systems and mountain fronts globally. Collectors look for unique 'puddingstone' varieties with colorful clasts.
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