File:Jasper breccia.jpg

English: Japser breccia (cut & polished surface)

Sedimentary rocks form by the solidification of loose sediments. Loose sediments become hard rocks by the processes of deposition, burial, compaction, dewatering, and cementation.

There are three categories of sedimentary rocks: 1) Siliciclastic sedimentary rocks form by the solidification of sediments produced by weathering & erosion of any previously existing rocks. 2) Biogenic sedimentary rocks form by the solidification of sediments that were once-living organisms (plants, animals, micro-organisms). 3) Chemical sedimentary rocks form by the solidification of sediments formed by inorganic chemical reactions. Most sedimentary rocks have a clastic texture, but some are crystalline.

Breccia is an uncommon, coarse-grained, siliciclastic sedimentary rock. Breccias form in many ways (sedimentary breccias, volcanic breccias, tectonic breccias/fault breccias, collapse breccias, boiling breccias, hydrothermal breccias, xenolith breccias, seismite breccias, injectite breccias, etc.), but they all have the same general appearance. Sedimentary breccias contain a mix of large & small grains. The large grains (gravel - pebbles or cobbles or boulders) are angular to subangular in shape, and they are surrounded by a finer-grained matrix, usually sand or mud.

The attractive breccia shown above contains abundant reddish- and yellowish-colored chert fragments surrounded by a very dark brown matrix of finer-grained material. Reddish-colored chert is sometimes called "jasper". I’m not sure of the provenance of this rock, but I suspect it comes from Arkansas or Oklahoma (corrections or verifications are welcome).