sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness: variable (3-7 Mohs depending on clasts/cement); Color: tan, brown, rusty orange, and white; Luster: earthy matrix with dull to vitreous clasts; Structure: clastic texture with rounded gravel-to-cobble sized fragments; Cleavage: none (breaks through or around clasts).
- Hardness
- variable (3-7 Mohs depending on clasts/cement)
- Color
- tan, brown, rusty orange, and white
- Luster
- earthy matrix with dull to vitreous clasts
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Physical properties
Hardness: variable (3-7 Mohs depending on clasts/cement); Color: tan, brown, rusty orange, and white; Luster: earthy matrix with dull to vitreous clasts; Structure: clastic texture with rounded gravel-to-cobble sized fragments; Cleavage: none (breaks through or around clasts).
Formation & geological history
Formed in high-energy environments like fast-moving rivers or alluvial fans where rounded pebbles and cobbles are deposited and later cemented by minerals like silica, calcite, or iron oxide. These can range from Precambrian to Holocene in age.
Uses & applications
Used primarily as coarse aggregate in construction, road fill, and sometimes as a decorative building stone or 'puddingstone' for landscaping and masonry.
Geological facts
Conglomerate is often called 'puddingstone' because the rounded pebbles look like fruit in a pudding. It is the sedimentary 'cousin' of Breccia, which contains angular fragments instead of rounded ones.
Field identification & locations
Identify in the field by looking for rounded, water-worn pebbles larger than 2mm embedded in a finer-grained matrix. Commonly found near ancient riverbeds, shoreline deposits, or mountain bases.
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