Earth’s inside crust is made up of pieces that move called plates.  As the plates move, they push and pull the rock underneath it.  Inside the Earth is scorching heat that can melt anything.  The deeper you go toward the center of the Earth, the hotter it gets.   As the plates move, they push down on igneous, sedimentary, and even metamorphic rock.  This causes the rock texture, color, or properties to change. It is a little like taking different colors of clay and mixing them.  The final color depends on what colors were mixed and how much of each color was added. 
     Sometimes new minerals are made when they are forced into other rock combinations. Metamorphism is how something changes over time.  Scientists can look at metamorphic rocks and figure out how they were made.  Sometimes the rocks are changed so much that scientists can’t figure it out at all.

Examples of metamorphic rocks:

Examples of minerals found in metamorphic rocks: