Mudrock composition

Mudrocks, by definition, consist of at least fifty percent mud-sized particles. Specifically, mud is composed of silt-sized particles that are between 1/16 – 1/256 of a millimeter in diameter, and clay-sized particles which are less than 1/256 millimeter.

Mudrocks contain mostly clay minerals and quartz ($S_{i}O_{2}$)and feldspars (a group of minerals including aluminum silicates of soda (sodium oxide), potassium (potassium oxide), or lime (calcium oxide)). They can also contain the following particles at less than 63 micrometres: calcite ($CaCO_{3}$), dolomite ($CaMgCO_{3}$), siderite ($FeCO_{3}$), pyrite ($FeS_{2}$), marcasite ($FeS_{2}$), heavy minerals, and even organic carbon.

The term "mudrock" allows for further subdivisions of siltstone, claystone, mudstone, and shale. For example, a siltstone would be made of more than 50-percent grains that equate to 1/16 - 1/256 of a millimeter. "Shale" denotes fissility, which implies an ability to part easily or break parallel to stratification. Siltstone, mudstone, and claystone implies lithified, or hardened, detritus without fissility.

Type	Min grain	Max grain
Claystone	0 µm	4 µm
Mudstone	0 µm	64 µm
Shale	0 µm	64 µm
Siltstone	4 µm	64 µm
Slate	na	na