sedimentary
Conglomerate
Clastic Sedimentary Rock (Conglomerate)
Hardness: variable (depends on clasts, often 6-7 if quartz-heavy); Color: multi-colored with a gray or tan matrix; Luster: dull/earthy matrix with glassy clasts; Structure: clastic/coarse-grained; Cleavage: none.
- Hardness
- variable (depends on clasts, often 6-7 if quartz-heavy)
- Color
- multi-colored with a gray or tan matrix
- Luster
- dull/earthy matrix with glassy clasts
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Physical properties
Hardness: variable (depends on clasts, often 6-7 if quartz-heavy); Color: multi-colored with a gray or tan matrix; Luster: dull/earthy matrix with glassy clasts; Structure: clastic/coarse-grained; Cleavage: none.
Formation & geological history
Formed through the lithification of rounded gravel and boulders (clasts) larger than 2mm, typically in high-energy environments like riverbeds, alluvial fans, or beaches. Geological age can range from Precambrian to Holocene.
Uses & applications
Used primarily in the construction industry as coarse aggregate for concrete and road stone. Rarely used in jewelry unless it contains semi-precious clasts (e.g., Puddingstone).
Geological facts
Conglomerates are often called 'puddingstone' because the rounded pebbles look like raisins in a pudding. They are key indicators for geologists of ancient high-speed water currents.
Field identification & locations
Identify in the field by looking for rounded, water-worn pebbles cemented into a finer matrix. Commonly found in sedimentary basins and ancient river courses. Collectors look for unique color contrasts between pebbles and matrix.
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