Mudstone; Argillite

Mudstone is a sedimentary rock that solidifies from mud and clay. The texture is soft, the degree of consolidation is low, and recrystallization is not obvious. Its composition and structure are similar to those of shale, but the bedding is not well-developed, and it is not easy to break. Mudstone is mainly composed of illite, and it often contains other clay minerals, clastic minerals, autogenous minerals, iron-manganese materials and organic matter. The common types include: (1) calcareous mudstone, which is common in continental red rock strata and marine and lagoon facies sedimentary rock layers with some calcium carbonate (content <25%); (2) iron mudstone, which is often found in red rock strata and contains substantial amounts of iron minerals, such as haematite, limonite and goethite; the main colours are red, purple or greyish green; (3) siliceous mudstone, which contains more SiO₂(up to 85% or more), no or little iron and carbonate materials, and always occurs with...