There are three ways that metamorphic rocks can form. The three types of metamorphism are Contact, Regional, and Dynamic metamorphism.

Contact Metamorphism occurs when magma comes in contact with an already existing body of rock. When this happens the existing rocks temperature rises and also becomes infiltrated with fluid from the magma. The area affected by the contact of magma is usually small, from 1 to 10 kilometers. Contact metamorphism produces non-foliated (rocks without any cleavage) rocks such as marble, quartzite, and hornfels.

In the diagram above magma has pushed its way into layers of limestone, quartz sandstone and shale. The heat generated by the magma chamber has changed these sedimentary rocks into the metamorphic rocks marble, quartzite, an hornfels.

Regional Metamorphism occurs over a much larger area. This metamorphism produces rocks such as gneiss and schist. Regional metamorphism is caused by large geologic processes such as mountain-building. These rocks when exposed to the surface show the unbelievable pressure that cause the rocks to be bent and broken by the mountain building process. Regional metamorphism usually produces foliated rocks such as gneiss and schist.

Dynamic Metamorphism also occurs because of mountain-building. These huge forces of heat and pressure cause the rocks to be bent, folded, crushed, flattened, and sheared.

Metamorphic rocks are almost always harder than sedimentary rocks. They are generally as hard and sometimes harder than igneous rocks. They form the roots of many mountain chains and are exposed to the surface after the softer outer layers of rocks are eroded away. Many metamorphic rocks are found in mountainous regions today and are a good indicator that ancient mountains were present in areas that are now low hill or even flat plains.

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