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Introduction to Metamorphic Rocks Tour

The purpose of this website is to provide simple and accurate explanations of metamorphic rocks and processes to the student and to the general public.   A number of images are included to enhance your understanding and appreciation of these fascinating rocks.

Metamorphic (meta=change, morphic=form) rocks form due to the alteration of preexisting rocks, often referred to as parent or precursor rocks.    The parent rock could be igneous, sedimentary, or even a metamorphic rock.    The image to the left shows the metamorphic rock quartzite and its parent rock, the sedimentary rock sandstone.    There are many types of metamorphic rocks, some of which are readily identifiable, and others that require a microscope and sound knowledge of mineralogy to identify.    

Metamorphic Rocks Tour will introduce you to the more common metamorphic rocks, and also provide information on the processes that cause metamorphism and the types of metamorphism that occur.   Before taking the tour, see the diagram and paragraphs below about the rock cycle for some background information on rocks.

THE ROCK CYCLE    According to the concept of the rock cycle, igneous, sedimentary and metamorphic rocks are constantly forming and being destroyed within and at the surface of Earth's crust.    Weathering of rocks exposed at the surface results from changes in temperature, chemical reactions triggered by water and natural acids, and biological activity.    These processes form loose sediment from solid rock, the beginning of the sedimentary phase of the rock cycle.    Rocks forced deep underground will eventually melt if temperature rises enough, returning the material to the igneous phase of the rock cycle.    

Generally speaking, the metamorphic phase of the rock cycle represents the gradual alteration of a rock from its original texture and/or composition.    This transition typically results from an increase in temperature and pressure as rocks become deeply buried underground.     Of course, if metamorphic rocks become heated past their melting points, their components will enter into the igneous phase of the rock cycle.    The opposite can occur due to tectonic uplift of the crust.    This can lead to rapid weathering and erosion of the rocks overlying metamorphic rocks, reducing temperature and pressure on the deeply- buried rocks, and stopping the metamorphism that was occuring.    Longterm uplift may even expose the metamorphic rocks to weathering at the surface, returning the material to the sedimentary phase of the rock cycle.   Note that this diagram appears courtesy of Ms. Holly Dodson, University of California at Santa Barbara.

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