sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness: Variable (consists of diverse rounded clasts in a fine-grained matrix); Color: Multicolored (browns, grays, reds); Luster: Dull to earthy; Structure: Clastic with rounded grains larger than 2mm; Specific Gravity: 2.6-2.9.
- Color
- Multicolored (browns, grays, reds)
- Luster
- Dull to earthy
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Physical properties
Hardness: Variable (consists of diverse rounded clasts in a fine-grained matrix); Color: Multicolored (browns, grays, reds); Luster: Dull to earthy; Structure: Clastic with rounded grains larger than 2mm; Specific Gravity: 2.6-2.9.
Formation & geological history
Formed in high-energy environments like riverbeds, alluvial fans, or beaches where water current is strong enough to transport large, rounded pebbles. Over time, these sediments are buried and lithified by a matrix of sand, silt, or chemical cement (calcite or silica).
Uses & applications
Primarily used as aggregate in the construction industry for roads and buildings. Occasionally used in architecture as decorative facing stone or as a source of the minerals contained within the pebbles (e.g., gold or diamonds found in ancient conglomerate beds).
Geological facts
Conglomerate is often nicknamed 'puddingstone' because the rounded pebbles look like raisins in a pudding. Identifying the composition of the pebbles can tell geologists exactly where the ancient river or glacier originated from millions of years ago.
Field identification & locations
Identify in the field by looking for rounded, water-worn pebbles larger than 2mm cemented together. It is commonly found in ancient riverbeds or mountain basins. For collectors, look for 'polygenic' samples with many different colorful rock types in one piece.
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