- a rock similar to sandstone but with a significant content of mud/silt; graywackes exhibits poor sorting and bedding, characteristic of minor water action
or dirty sandstone Sedimentary rock composed of sand-sized grains in a fine-grained clay matrix. The sand-sized grains frequently include rock fragments of wide-ranging mineralogies (e.g., pyroxenes, amphiboles, feldspars, and quartz). The clay matrix may constitute up to 50% of the volume. Of the clay minerals, chlorite and biotite are most abundant. The matrix tends to bind the grains strongly and form a relatively hard rock
Texturally and mineralogically immature sandstones that contain more than 15% clay minerals They may consist of angular to sub-rounded grains of quartz and feldspar, small pebbles, and a fine matrix of clay minerals, chlorite, and carbonate