sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness: variable depending on clasts (usually 3-7 Mohs); Color: tan, grey, brown; Luster: earthy/dull; Structure: clastic texture with rounded pebbles (>2mm) in a fine-grained matrix; Cleavage: none (fractures across matrix).
- Hardness
- variable depending on clasts (usually 3-7 Mohs)
- Color
- tan, grey, brown
- Luster
- earthy/dull
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Physical properties
Hardness: variable depending on clasts (usually 3-7 Mohs); Color: tan, grey, brown; Luster: earthy/dull; Structure: clastic texture with rounded pebbles (>2mm) in a fine-grained matrix; Cleavage: none (fractures across matrix).
Formation & geological history
Formed in high-energy environments such as riverbeds, alluvial fans, or beaches where water energy is strong enough to transport large pebbles. Over millions of years, these sediments are buried and lithified by pressure and mineral cement.
Uses & applications
Primarily used in the construction industry as coarse aggregate for concrete and road fill. Occasionally used as a decorative stone in architecture if the clasts are colorful.
Geological facts
Conglomerate rocks are sometimes referred to as 'puddingstone' because the rounded pebbles embedded in the matrix resemble raisins or plums in a pudding. They serve as a geological record of ancient river systems.
Field identification & locations
Identify in the field by looking for rounded, water-worn pebbles larger than 2mm bonded together by a natural cement. Common in mountain runoff areas and ancient basins. Collectors should look for 'Puddingstone' variants with contrasting colors.
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