sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness: variable based on clasts and cement (typically 6-7 if quartz-rich); Color: multicolored with shades of gray, brown, and tan; Luster: dull to earthy matrix; Crystal structure: non-crystalline (clastic); Cleavage: none; Specific gravity: 2.6-2.8.
- Color
- multicolored with shades of gray, brown, and tan
- Luster
- dull to earthy matrix
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Physical properties
Hardness: variable based on clasts and cement (typically 6-7 if quartz-rich); Color: multicolored with shades of gray, brown, and tan; Luster: dull to earthy matrix; Crystal structure: non-crystalline (clastic); Cleavage: none; Specific gravity: 2.6-2.8.
Formation & geological history
Formed by the lithification of rounded gravel and pebbles (clast size >2mm). These sediments are typically deposited in high-energy environments like fast-flowing rivers, alluvial fans, or beaches where water action rounds the rock fragments over time.
Uses & applications
Used as coarse aggregate in the construction industry, for building stone, and occasionally as decorative stone or 'puddingstone' for ornamental landscaping and jewelry if the clasts are colorful.
Geological facts
Often called 'puddingstone' due to its appearance resembling a fruit pudding. It is a key indicator of ancient high-energy water environments and can be found in rock sequences dating from the Proterozoic to the present.
Field identification & locations
Identify in the field by looking for large, rounded rock fragments (clasts) naturally cemented in a finer-grained matrix. Found globally in ancient riverbeds and mountain fronts. Collectors should look for unique clast compositions like jasper or quartz.
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