Well, after millions of years, the mud will start to cement together, due to natural cements and will form rock. This can result in footprints, fossils, animal remain, etc to be preserved in the rock.
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phyllite
If slate is sufficiently heated and compressed it becomes phyllite.
When mudstone is heated and subjected to pressure, it transforms into a type of metamorphic rock known as shale. With further heat and pressure, shale can metamorphose into slate, which is characterized by its fine-grained texture and ability to cleave into thin sheets. This process is part of the lithification and metamorphism of sedimentary rocks.
Gneiss.
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phyllite
If slate is sufficiently heated and compressed it becomes phyllite.
When mudstone is heated and subjected to pressure, it transforms into a type of metamorphic rock known as shale. With further heat and pressure, shale can metamorphose into slate, which is characterized by its fine-grained texture and ability to cleave into thin sheets. This process is part of the lithification and metamorphism of sedimentary rocks.
Gneiss.
Slate is already a metamorpic rock. It is formed by the action of heat and pressure on shale. Further metamorphism may produce phyllite.
Mudstone is sedimentary
Mudstone is a clastic sedimentary rock.
Mudstone is a clasitc sedimentary rock.
Mudstone is a mudrock. It is made of clay minerals and other very small pieces of rock. Mudstone is sedimentary.
The process is called Metamorphosis of Rocks. When the slate goes under the conditions of high pressure and heat it changes to schist or gneiss. Type of slate decide whether it gonna be schist or gneiss.
Phyllite is metamorphosed slate, which is also a metamorphic rock. Shale or mudstone is the protolith (parent rock) of slate.