Sedimentary rock
Oolite
Limestone made mostly of ooids (sand-sized grains of concentric calcite or aragonite layers).
In thin section
Concentric (and sometimes radial) layers around a nucleus such as a shell fragment or quartz grain.
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More photos and thin sections
Other sedimentary rocks
Conglomerate and breccia · Quartz arenite · Arkose · Lithic arenite · Wacke (greywacke) · Mudrocks: shale, mudstone, siltstone, claystone · Limestone · Chalk · Coquina · Travertine and tufa · Dolostone · Chert · Diatomite · Radiolarite · Evaporites: rock salt and gypsum · Banded iron formation · Coal: peat to anthracite · Oil shale