sedimentary
Conglomerate (with Jasper pebble)
Conglomerate / Microcrystalline Quartz (Jasper)
Hardness ranges from 6 to 7 on the Mohs scale for the jasper pebble and quartz grains. Color: reddish-brown pebble embedded in a tan to grayish sandy, sparkly matrix. Luster: vitreous to waxy on the smooth pebble, dull to glistening on the sandy matrix.…
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Physical properties
Hardness ranges from 6 to 7 on the Mohs scale for the jasper pebble and quartz grains. Color: reddish-brown pebble embedded in a tan to grayish sandy, sparkly matrix. Luster: vitreous to waxy on the smooth pebble, dull to glistening on the sandy matrix. Texture: clastic, medium-to-coarse grained with rounded clasts cemented together.
Formation & geological history
Formed in high-energy sedimentary environments such as river beds, alluvial fans, or beach shores where rounded pebbles like chert/jasper are deposited alongside coarse sand and subsequently cemented by silica or calcite over geological timescales.
Uses & applications
Used primarily in educational rock collections, landscaping, decorative stone, and aggregates for concrete. Well-rounded quartz/jasper pebbles within conglomerate can also be polished by rock hobbists.
Geological facts
Conglomerates are often referred to as 'puddingstones' when rounded reddish pebbles are vividly set against a light matrix. They preserve history about the energy of ancient rivers or shoreline environments.
Field identification & locations
Identified by rounded rock fragments (clasts) larger than 2 mm cemented within a finer-grained matrix. Look for distinct smooth pebbles sticking out of a rough sand-like stone in river valleys or sedimentary outcrop beds.
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