sedimentary
Conglomerate (Asphaltic/Anthropogenic)
Clastic sedimentary rock / Bituminous mixture
Hardness: 3-6 (variable based on aggregate); Color: Dark grey to black with lighter grey stone inclusions; Luster: Dull to sub-metallic; Crystal structure: Amorphous matrix with crystalline clasts; Cleavage: None (irregular fracture); Specific Gravity: 2.1-2.4.
- Hardness
- 3-6 (variable based on aggregate)
- Color
- Dark grey to black with lighter grey stone inclusions
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 3-6 (variable based on aggregate); Color: Dark grey to black with lighter grey stone inclusions; Luster: Dull to sub-metallic; Crystal structure: Amorphous matrix with crystalline clasts; Cleavage: None (irregular fracture); Specific Gravity: 2.1-2.4.
Formation & geological history
Formed through the lithification of rounded clasts (pebbles/gravel) cemented by a fine-grained matrix. Specimens like this one, found in disturbed soil, often represent anthropogenic 'puddingstone' or historical asphalt where bitumen binds natural stone. Geological ages for natural conglomerate vary from Precambrian to Holocene.
Uses & applications
Primarily used in construction as aggregate for roads, concrete, and building stone. Fine specimens of natural conglomerate (like Jasper Conglomerate) are used in jewelry and lapidary arts.
Geological facts
Natural conglomerates are often called 'puddingstones' because the stones look like raisins in a pudding. They are key indicators of high-energy past environments like fast-moving rivers or wave-swept beaches.
Field identification & locations
Identify by looking for rounded rock fragments larger than 2mm embedded in a finer matrix. Unlike breccia, the pieces are rounded rather than angular. Commonly found in old riverbeds, glacial till, and construction sites.
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