What are Metamorphic Rocks?
Metamorphic rocks are formed when existing rocks are changed by heat and/or pressure. This process causes partial melting and deformation in the rocks. Metamorphic rocks are grouped by their appearance
Groups of Metamorphic Rocks
Do they have layers or bands of crystals? If so, then they are called foliated. Slate, schist and gneiss are examples of this type of metamorphic rock.
Do they have a crystaline appearance without any banding? If so, then these rocks are called nonfoliated. Quartzite and marble are examples of nonfoliated metamorphic rocks.
Using the Metamorphic Rock Chart on page 7 in your reference tables.
This chart has a lot of information about metamorphic rocks and you should use it every time you encounter a question related to metamorphic rocks. For example, look at the comment column. The information given tells you the material the metamorphic rocks originally came from. This is called the parent material. Find marble on the chart, now look at the comments. The information tells us marble formed from limestone or dolostone. Now we know that a sedimentary rock was changed by heat and/or pressure into a metamorphic rock.
How do metamorphic rocks form?
Regional Metamorphic rocks usually form where there has been a mountain-building activity on the earth. These rocks are exposed when the mountain range above them has been eroded away.
Contact Metamorphic rocks occur in rocks that are very close to or in contact with an igneous intrusion. These rocks are found in a narrow area between the unchanged parent rock and newly formed igneous rock.
Use page 7 in your reference tables to answer the following questions.
1. Which mineral is found in the metamorphic rock gneiss?
chlorite, feldspar, olivine or halite
2. Which of the following metamorphic rocks generally contain foliated crystals?
quartzite, marble, schist or metaconglomerate
3. Which metamorphic rock generally contains the smallest crystals?
schist, gneiss, metaconglomerate or slate
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