Describe the process by which metamorphic rock can become sedimentary rock?

Answer 1

First the metamorphic schist would have to become exposed through means of uplift and erosion. Subjected to weathering, rock particles will become transported by wind and water, becoming smaller and smaller until they fit the definition of sand grain size. Rivers and streams will eventually transport the tiny particles to the continental shelf where they will sink to the bottom and be covered by additional layers of sand. Because of the weight of overlying layers, the sandgrains will undergo a process known as lithification, where excess water is squeezed out and a cementing mineral solution will bind the sand grains together. At this point it can be called sandstone.

Answer 2

There are many ways a sedimentary rock can become a metamorphic rock depending on the type of environment but in general metamorphism is any process that changes the mineral content/composition and/or microstructure of a rock which is caused by a change in physical conditions that become different then those under which the rock was originally formed.

So for either sedimentary or igneous this can be accomplished by changes in temperature, pressure, stress/deformation or metamorphic fluids.