Here's why:

* Metamorphic rocks are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are subjected to intense heat and pressure. This changes their mineral composition, texture, and often their overall appearance.

* Chlorite schist is specifically formed from the metamorphism of shale or basalt. The presence of chlorite, a green mineral, gives the schist its distinctive color and is a telltale sign of metamorphism.

Let me know if you have any other rock-related questions!