sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness varies by cement/clast (typically 6-7); Color: dark matrix with white/gray clasts; Luster: dull to earthy; Texture: coarse-grained with rounded clasts; Cleavage: none.
- Color
- dark matrix with white/gray clasts
- Luster
- dull to earthy
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Physical properties
Hardness varies by cement/clast (typically 6-7); Color: dark matrix with white/gray clasts; Luster: dull to earthy; Texture: coarse-grained with rounded clasts; Cleavage: none.
Formation & geological history
Formed through the lithification of rounded gravel and pebble-sized clasts. These are typically deposited in high-energy environments like riverbeds, beaches, or alluvial fans, often dating back millions of years depending on the stratigraphic layer.
Uses & applications
Used primarily in the construction industry as coarse aggregate for concrete and road base. Occasionally polished for use as ornamental stone or decorative gravel.
Geological facts
Conglomerate is often called a 'puddingstone' in certain regions of the UK and US due to its appearance. It is a key indicator for geologists that a high-energy water source once flowed through the area.
Field identification & locations
Identify in the field by looking for rounded pebbles (clasts) larger than 2mm embedded in a finer-grained matrix. It is commonly found in sedimentary basins and ancient river deposits. Collectors look for unique color contrasts between the matrix and pebbles.
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