sedimentary
Conglomerate
Clastic Sedimentary Conglomerate (SiO2, CaCO3, etc.)
Hardness: variable (matrix 3-7, clasts 6-7); Color: tan, grey, or brown matrix with multicolored rounded clasts; Luster: dull/earthy matrix; Crystal structure: none (clastic); Cleavage: none; Specific gravity: 2.3 - 2.8
- Hardness
- variable (matrix 3-7, clasts 6-7)
- Color
- tan, grey, or brown matrix with multicolored rounded clasts
- Luster
- dull/earthy matrix
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Physical properties
Hardness: variable (matrix 3-7, clasts 6-7); Color: tan, grey, or brown matrix with multicolored rounded clasts; Luster: dull/earthy matrix; Crystal structure: none (clastic); Cleavage: none; Specific gravity: 2.3 - 2.8
Formation & geological history
Formed in high-energy environments like riverbeds, alluvial fans, or beaches where water rounds the stones. Large clasts are deposited and later cemented by minerals like silica, calcite, or iron oxide during lithification.
Uses & applications
Used in the construction industry as coarse aggregate for concrete and roadbeds; some colorful varieties are used as decorative stone or for landscaping.
Geological facts
Conglomerate is often called 'puddingstone' due to its resemblance to fruit cake or Christmas pudding. It records the historical path and speed of ancient water systems.
Field identification & locations
Identify in the field by looking for rounded, smooth pebbles (clasts) larger than 2mm embedded in a finer-grained matrix. Often found in ancient river basins and mountain foot-slopes.
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