Linked from
The 6 pages that link to Mudstone, each with the reason it gives.
ShaleCompared with: Its similar composition but weaker tendency to split separates it from shale.
SlateRelated: Mudstone can become slate when burial and tectonic pressure alter its fabric.
MudrockBroader topic: Mudstone is a non-fissile mudrock, unlike shale.
Clastic rockBroader topic: Mudstone is a clastic alternative to fissile shale among mud-rich rocks.