A rock composed of siliciclastic mud but with carbonate cement should be treated as one of the fine-grained siliciclastic rocks ("shale", claystone, mudstone, siltstone). wackestone: a limestone composed of lime mud (micrite) and greater than 10% grains (ooids, peloids, bioclasts, or intraclasts). read more
Well, shales tend to break into thin, angular pieces whereas limestones tend to break into hard blocks. While mudstones also break into blocky pieces, they tend to be quite soft. read more
Mudstone Mudstone is an extremely fine-grained sedimentary rock consisting of a mixture of clay and silt-sized particles. Terms such as claystone and siltstone are often used in place of mudstone, although these refer to rocks whose grain size falls within much narrower ranges and under close examination these are often technically mudstones. read more
Limestone is made up of calcium carbonate (fizzes with acid). This may be shell fragments, mud, or small, round ooliths that form in tropical lagoons. Chalk is a soft white limestone made from the microscopic skeletons of marine plankton. read more