Download Sedimentary-Rock-Classification

Sedimentary Rock
Classification
Dana Desonie, Ph.D.
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Printed: February 28, 2013
AUTHOR
Dana Desonie, Ph.D.
www.ck12.org
C ONCEPT
Concept 1. Sedimentary Rock Classification
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Sedimentary Rock
Classification
• Describe how sedimentary rocks are classified.
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. Clastic sedimentary rocks are made of sediments. The
sediments differ in size. Chemical sedimentary rocks are made of minerals that precipitate from saline water.
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
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.
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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.
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)
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Concept 1. Sedimentary Rock Classification
TABLE 1.2: (continued)
Picture
Rock Name
Breccia
Type of Sedimentary Rock
Clastic
Sandstone
Clastic
Siltstone
Clastic
Shale
Clastic
Rock Salt
Chemical precipitate
Rock Gypsum
Chemical precipitate
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TABLE 1.2: (continued)
Picture
Rock Name
Dolostone
Type of Sedimentary Rock
Chemical precipitate
Limestone
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.
Practice
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 for more content.
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Concept 1. Sedimentary Rock Classification
List the three types of sedimentary rocks.
List the characteristics of clastic rocks.
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?
How do chemical rocks form?
What are bioclastic rocks?
List the two types of biocalstic rocks.
Review
1. Describe the two main types of sedimentary rocks.
2. Compare and contrast chemical sedimentary rocks and clastic sedimentary rocks.
3. List sedimentary rock types by grain size, from small to large.
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