 Welcome to Open Geology. This is a project to share geology with everybody. This was created by a group of Salt Lake Community College instructors and partially funded by Salt Lake Community College, though these videos do not reflect the views of the college. This is a Creative Commons video. Today we'll be talking about metamorphism and metamorphic rocks. This is chapter 6 of the OpenGeology.org textbook. Metamorphic rocks are one of the three major rock groups, sedimentary, igneous, and metamorphic. Metamorphic rocks are derived from the addition of heat, pressure, or fluids to change a rock from its original state into a different rock. And so that brings us to this question, what does metamorphism mean and what would cause metamorphism in rocks? So let's kind of talk about each one of these. Metamorphism is essentially a way of saying change, change from one rock into another. It's a word you may have heard used for butterflies when they change from a caterpillar to a chrysalis to a butterfly. You can change one rock into another with heat, pressure, or fluids. And a rock is generally happy in certain conditions. What I mean by that is a mineral with its crystalline structure and elements in it are generally in equilibrium with the environment that it's in. And if you change that environment, you offset that equilibrium. And those minerals have to readjust to be in equilibrium again with the new environment. And so what you'll get if you apply these heat, pressure, or fluids is you'll get new and very interesting minerals. And the cool thing about metamorphic rocks is they tell you a story of the changing forces of that area. And it's all embedded in the mineralogy of these metamorphic rocks. So let's talk about the protolith. Protolith is the before protolith rock, the first rock. This is the rock that existed before metamorphism occurred. And it could be an igneous, sedimentary, or a different type of metamorphic rock. And then heat and pressure was applied to one of these rocks and you get the metamorphic rock. Let's look at an example. Here you have a photo micrograph of some beautiful quartz grains. Once a certain amount of heat and maybe pressure is applied, all of the quartz grains no longer have pores between them. They're fused together, they've been recrystallized, and now you have this beautiful quartzite. So how does the metamorphic rock differ from the protolith? What do you think? Do you think the chemistry of the rock is different? Unless chemicals have been added or taken away from the rock, the chemistry of the rock should be the same. You're just reorganizing the atoms in the rock to make different minerals. So minerals will or can be different but the elements are the same. With the exception of the case of fluids as a way to change a rock, metamorphosa rock, fluids typically involve the addition or subtraction of elements from that rock which can in turn change the chemistry. Like I said earlier, the minerals in the rock will determine, can tell you what kind of metamorphosing agent, be it pressure or fluids or heat, caused the change and how much of that was applied to create that change and that in turn will tell us the story of the metamorphic rock. So next we'll talk about where metamorphism generally happens. Thank you.