Created 06/19/2013 03:36 PM
Metamorphic rocks are among the most interesting and diverse types of rocks found in the Earth's crust. Metamorphic rocks are formed when sedimentary, igneous, or even pre-existing metamorphic rocks undergo changes in pressure, temperature, or chemical environment due to the action of tectonic forces. These changes can cause the rock to take on new characteristics, leading to the creation of a new metamorphic rock.
Identifying metamorphic rocks can be difficult, as they often appear similar to other types of rocks. However, there are several distinct characteristics that can help you determine if a rock is metamorphic. In this article, we will explore the various types of metamorphic rocks and how to identify them.
The first type of metamorphic rock is foliated metamorphic rock. This rock is characterized by having a layered appearance, as if it has been split into thin layers. This layered appearance is caused by the action of pressure on preexisting rock, which causes minerals to align along planes of weakness. Common examples of foliated metamorphic rocks include slate, schist, and gneiss.
Slate is a type of foliated metamorphic rock that forms when sedimentary rocks like mudstone, shale, or volcanic ash are subjected to high pressures and temperatures. Schist is another type of foliated metamorphic rock, which is created when a sedimentary or igneous rock is subjected to higher pressures and temperatures. Gneiss is the most common type of foliated metamorphic rock, and is created when a pre-existing rock is subjected to the highest pressures and temperatures.
The second type of metamorphic rock is non-foliated metamorphic rock, which does not have the layered appearance of foliated metamorphic rock. Non-foliated metamorphic rock is created when preexisting rock is subjected to heat and pressure, but not to the same degree as foliated metamorphic rocks. Examples of non-foliated metamorphic rock include marble, quartzite, and hornfels.
Marble is a type of non-foliated metamorphic rock that forms when preexisting limestone or dolomite rocks are heated and pressured. Quartzite is another type of non-foliated metamorphic rock and is created when preexisting sandstone is subjected to high temperatures and pressures. Hornfels is the third type of non-foliated metamorphic rock, and is created when preexisting mudstone or shale is heated and pressured.
In order to identify metamorphic rock, it is important to look for certain characteristics. Foliated metamorphic rocks will have a layered or striped appearance, while non-foliated metamorphic rocks will often have a smooth, glossy surface. Additionally, the minerals within a metamorphic rock will often be aligned in bands or streaks, which is another indication that a rock is metamorphic.
It is also important to note that metamorphic rocks often contain fossils, which can help in determining the age of the rock. Additionally, some metamorphic rocks may contain a variety of minerals, which can provide clues to its origin.
Finally, when examining a rock, it is important to determine whether it is igneous, sedimentary, or metamorphic. Igneous rocks are formed when molten rock cools and solidifies, while sedimentary rocks are created from the accumulation of sediment over time. Metamorphic rocks, on the other hand, are created when pre-existing rocks are subjected to high pressures and temperatures.
In conclusion, metamorphic rocks are among the most interesting and diverse types of rocks found in the Earth's crust. They are created when pre-existing rocks are subjected to high pressures and temperatures, and can be identified based on their layered or striped appearance, the alignment of minerals, and the presence of fossils. By understanding the different types of metamorphic rocks and how to identify them, you can gain a greater appreciation for the Earth's geological history.
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