What does mudstone mean?
Mudstone is a fine-grained sedimentary rock made from mud that has been buried, compacted, and hardened into stone. It commonly contains clay minerals and tiny particles of silt, and it often preserves fossils because its fine texture can trap the remains of organisms. Geologists distinguish mudstone from shale by its structure: mudstone is generally more massive and does not split readily into thin layers, whereas shale is fissile. Mudstone can form in a range of aquatic environments, including quiet seas, lakes, and river floodplains, so its layers provide evidence about past climates and landscapes. The word is used particularly in geology and earth science, and is recognized in both British and American English. It is also broader than the general word “stone” because it identifies a specific sedimentary material with characteristic texture and composition.
nounA fine-grained sedimentary rock formed from compacted and lithified mud, commonly containing clay and silt. Mudstone is distinguished from shale mainly by the degree to which it splits into layers.
- A sedimentary rock formed from compacted and lithified mud, especially a fine-grained, clay-rich rock that does not readily split into layers.
"The cliff exposes a thick sequence of mudstone containing fossilized shells."
"Geologists found layers of mudstone beneath the valley floor."
"The museum displays a fossil ammonite preserved in mudstone."
The plural is used for individual rock formations or specimens of mudstone.
"Several mudstones from the quarry are displayed in the geology collection."
Mudstone is a time capsule: its layers can preserve fossils and reveal the environments in which ancient seas, rivers, and lakes deposited mud.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does mudstone come from?
The word is a transparent compound of “mud” and “stone,” combining the material with the term for the resulting hardened rock. The compound has been in use since the early modern period, when English speakers were already forming numerous geological and mineralogical compounds in this way. Its formation follows the ordinary English pattern of joining two familiar nouns to name a specific kind of object.
How mudstone is actually used
In geology, the term is especially common in British and international usage. It overlaps with mudrock, although some geological classifications use the terms in slightly different senses.
Easily confused with mudstone
Both are fine-grained sedimentary rocks, but shale is fissile and tends to split readily into thin layers, whereas mudstone is generally more massive and less easily split.