A sedimentary rock can become a metamorphic rock through the process of metamorphism, which involves the transformation of existing rocks due to changes in temperature, pressure, and/or chemical environment.
The rock cycle diagram shows that sedimentary rocks are formed from the weathering and erosion of pre-existing rocks, which are then transported and deposited in layers. Over time, these layers can become compacted and cemented together, forming a sedimentary rock.
If this sedimentary rock is then subjected to high temperatures and/or pressures, such as through burial deep within the Earth's crust, it can undergo metamorphism. During metamorphism, the minerals in the rock can undergo changes in composition and/or texture, resulting in a new rock with different physical and chemical properties.
For example, a shale sedimentary rock could be subjected to high temperatures and pressures, causing the clay minerals within the rock to recrystallize into new minerals such as mica or quartz. This would result in a new metamorphic rock such as slate or phyllite.
Therefore, through the process of metamorphism, a sedimentary rock can be transformed into a new metamorphic rock with different physical and chemical properties.