When sedimentary rock is changed by heat or pressure, it forms metamorphic rock.

Here's why:

* Sedimentary rocks are formed from the accumulation and cementation of sediments.

* Metamorphism is a process where existing rocks (like sedimentary rocks) are transformed by intense heat and/or pressure. These conditions cause changes in the rock's mineral composition, texture, and sometimes even chemical composition.

So, the heat and pressure essentially "bake" the sedimentary rock, creating a new type of rock with different characteristics.