sedimentary
Conglomerate
Conglomerate (Sedimentary rock containing rounded clasts)
Hardness: Variable based on cementation and clasts (usually 3-7 Mohs); Color: Tan, brown, ochre, rusty-yellow; Luster: Dull or earthy matrix with various clast lusters; Crystal Structure: Clastic (non-crystalline matrix); Cleavage: None (breaks across clasts).
- Hardness
- Variable based on cementation and clasts (usually 3-7 Mohs)
- Color
- Tan, brown, ochre, rusty-yellow
- Luster
- Dull or earthy matrix with various clast lusters
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Physical properties
Hardness: Variable based on cementation and clasts (usually 3-7 Mohs); Color: Tan, brown, ochre, rusty-yellow; Luster: Dull or earthy matrix with various clast lusters; Crystal Structure: Clastic (non-crystalline matrix); Cleavage: None (breaks across clasts).
Formation & geological history
Formed by the lithification of rounded gravel and pebbles, typically in high-energy environments like riverbeds, alluvial fans, or beaches where water transport rounds the fragments of older rocks.
Uses & applications
Used primarily in the construction industry as fill material, coarse aggregate for concrete, and occasionally as a decorative architectural stone or 'puddingstone' for landscaping.
Geological facts
Conglomerate is often called 'nature's concrete' because it looks like man-made cement with gravel mixed in. It is an excellent indicator of ancient river systems and water flow velocity.
Field identification & locations
Identify by looking for rounded rock fragments (clasts) larger than 2mm embedded in a finer-grained matrix. It is commonly found in areas of ancient sedimentary basins or near mountain fronts.
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