What is one form from which a rock can change and one form into which it can change?

The lithological cycle or rock cycle is a concept of geology that describes the transitions of material in geological time that allow all rock to be transformed into one of three types: sedimentary rocks, metamorphic rocks and igneous rocks. [1] Rocks can pass through any of the three states when they are forced to break the balance. An igneous rock such as basalt can disintegrate and alter when exposed to the atmosphere, or re-melt when subducting below a continent. Due to the generating forces of the rock cycle, tectonic plates and the water cycle, the rocks cannot be kept in balance and are forced to change in the face of new environments. The rock cycle is a model that explains how the three types of rocks come from some other, and how the process changes from one type to another over time. The time for a rock to complete the phases is millions of years, and in the life of the Earth not all rocks can complete it.