Here's why:

* The Rock Cycle: The rock cycle involves rocks transforming from one type to another (igneous, sedimentary, metamorphic). These transformations happen through processes like melting, cooling, weathering, erosion, compaction, and heat and pressure.

* Matter Isn't Created or Destroyed: While the form of the rocks changes, the actual matter that makes up the rocks (minerals, elements) remains the same. It just gets rearranged and reorganized.

Think of it like baking a cake. You start with flour, sugar, eggs, etc. When you bake it, the ingredients change form, but the total amount of matter stays the same.