Mudrocks are a class of fine grained siliciclastic sedimentary rocks. The varying types of mudrocks include: siltstone, claystone, mudstone, slate, and shale. Most of the particles are less than 0.0625 mm (1/16th mm or 0.0025 inches) and are too small to study readily in the field. At first sight the rock types look quite similar; however, there are important differences in composition and nomenclature. There has been a great deal of disagreement involving the classification of mudrocks. There are a few important hurdles to classification, including:

1. Mudrocks are the least understood, and one of the most understudied sedimentary rocks to date
2. It is difficult to study mudrock constituents, due to their diminutive size and susceptibility to weathering on outcrops
3. And most importantly, there is more than one classification scheme accepted by scientists