sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness: variable depending on clasts (usually 6-7 if quartz-rich); Color: multicolored clasts in a brown, tan, or gray matrix; Luster: dull to earthy matrix with potentially vitreous clasts; Structure: clastic texture with rounded gravel-sized grains (>2mm) cemented together; Cleavage: none.
- Hardness
- variable depending on clasts (usually 6-7 if quartz-rich)
- Color
- multicolored clasts in a brown, tan, or gray matrix
- Luster
- dull to earthy matrix with potentially vitreous clasts
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Physical properties
Hardness: variable depending on clasts (usually 6-7 if quartz-rich); Color: multicolored clasts in a brown, tan, or gray matrix; Luster: dull to earthy matrix with potentially vitreous clasts; Structure: clastic texture with rounded gravel-sized grains (>2mm) cemented together; Cleavage: none.
Formation & geological history
Formed in high-energy environments such as riverbeds, alluvial fans, or beaches where water movement is strong enough to round large pebbles. Over time, these sediments are buried and lithified by mineral cements like calcite, silica, or iron oxide.
Uses & applications
Commonly used as a coarse aggregate in the construction industry for concrete and roads. Occasionally cut and polished as decorative stone or used in landscaping.
Geological facts
Conglomerate is often referred to as 'puddingstone' by collectors because the rounded pebbles look like raisins or fruit in a pudding. It is an indicator of ancient high-energy water systems.
Field identification & locations
Identify in the field by looking for 'concrete-like' appearance with large, smooth, rounded stones embedded in a finer-grained sandy/silty matrix. Found globally in ancient river basins and mountain-front deposits.
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