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Geosciences LibreTexts

11: Metamorphic Rocks

  • Page ID
    5661
  • Learning Objectives

    After completing this chapter, you should be able to:

    • Correctly identify the metamorphic rocks and their distinguishing features.
    • Identify foliated metamorphic rocks and the type of foliation. 
    • Determine the grade of metamorphism based on foliation and possible index minerals.
    • Recognize metamorphic environments and types of metamorphism.

    • 11.1: Introduction
      In any introductory textbook on physical geology, the reader will find the discussion on metamorphic rocks located after the chapters on igneous and sedimentary rocks, and for very good reason. Metamorphic rocks form by the physical and sometimes chemical alteration of a pre-existing rock, whether it is igneous or sedimentary. In some cases, even metamorphic rocks can be altered into a completely different metamorphic rock.
    • 11.2: Agents of Metamorphism
      All rocks beneath the surface of the earth experience an increase in pressure due to the weight of the overlying sediment and rock layers, and with increasing depth there is a corresponding increase in pressure. This increased pressure does not necessarily cause a rock to become metamorphic, because this particular pressure is typically equal in all directions and is known as lithostatic pressure.
    • 11.3: Metamorphic Rock Names
      As mentioned previously, differential pressures can cause a foliation to develop in metamorphosed rocks. There are a few types of foliations that are commonly seen in metamorphic rocks, each foliation type is dependent on the minerals that define the foliation. One type is described as a layering of dark and light-colored minerals so that the foliation is defined as alternating dark and light mineral bands throughout the rock.
    • 11.4: Lab Exercise (Part A)
      In order to answer the questions in this lab, you will need the rock samples from your HOL rock kit that are labeled M1 through M7 (located in the metamorphic rock bag). A photo of these samples is given in Figure 11.10. You will also need your hand lens, glass plate, and the HCl bottle.
    • 11.5: Types of Metamorphism
      Metamorphism that affects entire rock bodies over a broad region is referred to as regional metamorphism. There is a wide range of conditions in temperature and pressure that produce a wide range of metamorphic rock types. For example, all of the foliated rocks fall into this metamorphic category and some non-foliated rocks as well. The main point is that a large area is affected by changes in temperature and/or pressure.
    • 11.6: Lab Exercise (Part B)
      For this portion of the lab, you will be using Google Earth, and Figure 11.11 in this chapter. You will also need your rock samples M1 and M7.
    • 11.7: Student Responses
      The following is a summary of the questions in this lab for ease in submitting answers online.

    Thumbnail: Marble is a metamorphic rock composed of recrystallized carbonate minerals. While the foundation of the Parthenon in the Athenian Acropolis is composed of limestone, the columns were made of marble. Thumbnail: Parthenon, Athens Greece. Image used with permission (CC BY 2.0; Steve Swayne).