sedimentary
Conglomerate
Conglomerate (clastic sedimentary rock)
Hardness: 6-7 (individual clasts usually quartz), Color: Mixed (browns, tans, whites, reds), Luster: Dull to waxy, Crystal structure: Clastic (non-crystalline matrix), Cleavage: None, Specific gravity: 2.6-2.8
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Physical properties
Hardness: 6-7 (individual clasts usually quartz), Color: Mixed (browns, tans, whites, reds), Luster: Dull to waxy, Crystal structure: Clastic (non-crystalline matrix), Cleavage: None, Specific gravity: 2.6-2.8
Formation & geological history
Formed in high-energy environments like riverbeds or beaches where rounded gravel and pebbles are deposited and eventually cemented together by minerals like silica or calcite. Age varies from Proterozoic to Cenozoic.
Uses & applications
Used as aggregate in construction, as decorative stone in landscaping, or as architectural facade. High-quality specimens with colorful jasper or quartz inclusions are used by lapidaries for jewelry and paperweights.
Geological facts
Conglomerate is often called "puddingstone" because the dark matrix and lighter rounded stones resemble a traditional fruit pudding. It is an indicator of ancient river systems or shoreline environments.
Field identification & locations
Identify by the presence of rounded, water-worn clasts (pebbles) larger than 2mm bonded within a finer matrix. Found globally in ancient river basins and coastal mountain ranges. Collectors look for unique color contrasts between pebbles and matrix.
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