Can someone please help with this question from my school homework

Question

In addition to the pressure and temperature, what strongly influences the types of minerals that grow in a metamorphic rock? 

Answer 1

Hi Sam, 

The provenance of the metamorphic rock (essentially what the rock was before it was metamorphosed into something new) strongly influences what types of minerals grow in a metamorphic rock. 

For example, if you add heat and pressure to a sandstone which only contains quartz, it does not contain the necessary elements to form common metamorphic minerals (like kyanite, staurolite, biotite, garnet, etc.)

-Mike