What rock formed in mud when it is cemented and compressed?

The rock that forms from mud when it is cemented and compressed is called shale. Shale is a type of sedimentary rock that typically consists of clay minerals and silt-sized particles. Over time, layers of mud accumulate, and as they undergo lithification through compaction and cementation, they transform into shale. This process often occurs in environments such as river deltas, lake beds, and ocean floors.