sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness: variable (3-7 Mohs depending on clasts/cement); Color: multicolored with a gray, brown, or tan matrix; Luster: dull/earthy; Structure: clastic texture with rounded gravel-sized grains (clasts) larger than 2mm; Specific Gravity: 2.1-2.9.
- Hardness
- variable (3-7 Mohs depending on clasts/cement)
- Color
- multicolored with a gray, brown, or tan matrix
- Luster
- dull/earthy
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Physical properties
Hardness: variable (3-7 Mohs depending on clasts/cement); Color: multicolored with a gray, brown, or tan matrix; Luster: dull/earthy; Structure: clastic texture with rounded gravel-sized grains (clasts) larger than 2mm; Specific Gravity: 2.1-2.9.
Formation & geological history
Formed by the lithification of rounded gravel and pebbles, typically in high-energy environments such as riverbeds, alluvial fans, or beaches where water action rounds the stones. These formations can date from any geological era where water transport occurred.
Uses & applications
Used primarily as heavy aggregate in the construction industry for road beds, concrete, and fill. Occasionally used as dimension stone or decorative masonry if the clasts are colorful (e.g., 'puddingstone').
Geological facts
Conglomarate is often called 'puddingstone' because the rounded pebbles look like raisins in a pudding. It is the sedimentary 'cousin' of Breccia, which contains angular rather than rounded fragments.
Field identification & locations
Identify in the field by looking for a 'natural concrete' appearance with rounded stones firmly embedded in a finer-grained matrix. Commonly found in ancient river systems; popular with beginners due to the visible variety of embedded minerals.
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