sedimentary
Conglomerate
Conglomerate (Detrital sedimentary rock)
Hardness: 6.5-7 (highly variable based on clast composition); Color: Gray/beige matrix with brown and black rounded clasts; Luster: Dull/Earthy; Crystal Structure: None (clastic texture); Cleavage: None; Specific Gravity: 2.6-2.8
- Hardness
- 6
- Color
- Gray/beige matrix with brown and black rounded clasts
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6.5-7 (highly variable based on clast composition); Color: Gray/beige matrix with brown and black rounded clasts; Luster: Dull/Earthy; Crystal Structure: None (clastic texture); Cleavage: None; Specific Gravity: 2.6-2.8
Formation & geological history
Formed in high-energy environments like riverbeds or alluvial fans where water current is strong enough to transport large, rounded pebbles. Over time, these pebbles are buried and cemented together by minerals like silica or calcite. Age varies by formation location.
Uses & applications
Used primarily as aggregate in the construction industry for concrete and roadbeds. Some attractive specimens are used for ornamental stone or lapidary work.
Geological facts
Conglomerate is often called "puddingstone" because the rounded clasts resemble raisins or fruit in a pudding. It is the sedimentary opposite of breccia, which contains sharp, angular fragments.
Field identification & locations
Identify in the field by looking for rounded pebbles (larger than 2mm) embedded in a finer-grained matrix. Commonly found in ancient river channels or mountain base deposits. Collectors look for unique color contrasts between the pebbles and matrix.
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