Download Sedimentary Rock Classification

Sedimentary Rock
Classification
Dana Desonie, Ph.D.
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Printed: December 14, 2014
AUTHOR
Dana Desonie, Ph.D.
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C HAPTER
Chapter 1. Sedimentary Rock Classification
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Sedimentary Rock
Classification
• Describe how sedimentary rocks are classified.
• List some common sedimentary rocks.
Can you tell which type of rock these are?
If you look up close, you would be able to see grains of sand. From this distance, you can see different layers from
where the sand was laid down. This rock is sandstone. The sand grains are cemented together to make sandstone.
Sandstone is a common type of sedimentary rock.
Types of Sedimentary Rocks
The main types of sedimentary rocks are clastic or chemical. Some sedimentary rocks are a third type, organic.
Clastic sedimentary rocks are made of sediments. The sediments differ in size. Chemical sedimentary rocks are made
of minerals that precipitate from saline water. Organic sedimentary rocks are made from the bodies of organisms.
Clastic Sedimentary Rocks
Clastic sedimentary rocks are grouped by the size of the sediment they contain. Conglomerate and breccia are
made of individual stones that have been cemented together. In conglomerate, the stones are rounded. In breccia, the
stones are angular. Sandstone is made of sand-sized particles. Siltstone is made of smaller particles. Silt is smaller
than sand but larger than clay. Shale has the smallest grain size. Shale is made mostly of clay-sized particles and
hardened mud.
TABLE 1.1: Sedimentary Rock Sizes and Features
Rock
Conglomerate
Breccia
Sandstone
Siltstone
Shale
Sediment Size
Large
Large
Sand-sized
Silt-sized, smaller than sand
Clay-sized, smallest
Other Features
Rounded
Angular
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When sediments settle out of calmer water, they form horizontal layers. One layer is deposited first, and another
layer is deposited on top of it. So each layer is younger than the layer beneath it. When the sediments harden, the
layers are preserved.
Chemical Sedimentary Rocks
Sedimentary rocks formed by the crystallization of chemical precipitates are called chemical sedimentary rocks.
Dissolved ions in fluids precipitate out of the fluid and settle out, just like the halite pictured below ( Figure 1.1).
FIGURE 1.1
The evaporite, halite, on a cobble from the Dead Sea, Israel.
Living creatures can help chemicals become sedimentary rocks. Limestone is an example.
Organic Sedimentary Rocks
The bodies of organisms can make a sedimentary rock. Plant bodies are lithified to become coal. When shells are
cemented together they make a type of limestone. So limestone can be considered chemical or organic.
Some Common Sedimentary Rocks
Listed below are some common types of sedimentary rocks ( Table 1.2).
TABLE 1.2: Common Sedimentary Rocks
Picture
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Rock Name
Conglomerate
Type of Sedimentary Rock
Clastic (fragments of non-organic
sediments)
Breccia
Clastic
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Chapter 1. Sedimentary Rock Classification
TABLE 1.2: (continued)
Picture
Rock Name
Sandstone
Type of Sedimentary Rock
Clastic
Siltstone
Clastic
Shale
Clastic
Rock salt
Chemical precipitate
Rock gypsum
Chemical precipitate
Dolostone
Chemical precipitate
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TABLE 1.2: (continued)
Picture
Rock Name
Limestone
Type of Sedimentary Rock
Bioclastic (sediments from organic
materials, or plant or animal remains)
Coal
Organic
Vocabulary
• chemical sedimentary rocks: Rocks that form from the hardening of chemical precipitates.
• clastic sedimentary rocks: Rocks that form from hardening of sediments by compaction and/or cementation.
Summary
• Sediments settle out of water in horizontal layers.
• Clastic sedimentary rocks are classified based on how they form and on the size of the sediments.
• Chemical sedimentary rocks precipitate from fluids.
Explore More
Use the resource below to answer the questions that follow.
• Sedimentary Rocks at http://www.youtube.com/watch?v=Ox_3z_lW-Hw (7:13)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/1608
1.
2.
3.
4.
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7.
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List the three types of sedimentary rocks.
Where and how are clastic rocks found?
How do clastic rocks form?
Contrast conglomerates and breccia rocks.
What can be found in clastic rocks?
Explain the difference between layers and bands.
What can we learn from sedimentary rocks?
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Chapter 1. Sedimentary Rock Classification
8. How do chemical rocks form?
9. What are bioclastic rocks?
10. List the two types of biocalstic rocks.
Review
1. Describe the three main types of sedimentary rocks.
2. How can different types of limestone be bioclastic, chemical and organic?
3. List sedimentary rock types by grain size, from small to large.
References
1. Mark A. Wilson (Department of Geology, The College of Wooster). Halite forming on a rock in the Dead Sea.
Public Domain
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