Problem 1:
General Procedure for PART 4:
1) Observe and document the characteristics of 10 sedimentary rocks in the above videos.
Links to videos:
2) Enter your descriptions of your 10 rocks into the Sedimentary Rock Characteristics Fill-In Table below. (CHART in the files)
To receive full credit for your table, the entire table should be filled in. If there is no information to enter into the cell, please write “n/a” for does not apply.
3) When you think you have enough of your table completed, refer to this SEDIMENTARY ROCK NAMING CHART to find the names of each of the 10 rocks.
Rock Identification Procedure
Examine the SEDIMENTARY ROCK NAMING CHART to answer the following questions. The chart shows the names of common sedimentary rocks, including clastic, chemical, and biochemical rocks. Clastic Rocks are shown on the first page (Table 1). Chemical and biochemical rocks are shown on the second page (Table 2).
Clastic Sedimentary Rocks
These rocks are composed of clasts (fragments of minerals or rocks) derived from pre-existing rock. The composition, size, shape and sorting of the clasts, as well as the cement that holds them together, are significant characteristics of clastic rocks.
Clastic rock names are classified according to predominant clast size. Clastic rocks may consist of almost any assemblage of mineral or rock fragment. Most sandstone, for instance, is rich in quartz, but it may also contain considerable feldspar, or ferromagnesian minerals. Shale is usually composed largely of clay but may also contain considerable calcite or even quartz. A classification scheme based on the average size of clastic particles in sedimentary rocks is given on pages 150 and 167 of your textbook.
Chemical Sedimentary Rocks
This category of rocks form through precipitation of minerals a saturated solution. Common minerals in chemical sedimentary rocks are calcite, dolomite, gypsum, halite, hematite, and silica (chalcedony). Most rocks of this type are composed of only one mineral. Therefore, the rock composition is identical to the mineral composition in these rocks.
Biochemical Sedimentary Rocks
These rocks are composed of accumulated minerals, shells, or skeletal remains derived from once living organisms. The remains of the organisms may be easily visible and identifiable (such as clam shell fragments) or may be microscopic (such as plankton shells). While not technically considered rocks, petroleum, coal, and peat are considered biochemical/organic sedimentary products.
Instructions for reading the SEDIMENTARY ROCK NAMING CHART:
First, determine whether the rock is clastic, biochemical, or chemical.
Use Table 1 for clastic rocks: Your rock sample is clastic if it is composed of small fragments of other rock or minerals.
Use Table 2 for chemical and biochemical rocks: If the rock is clearly made of interlocking crystals or appears very dense and massive, then it may be chemical. If the rock has visible organic matter or fossils it may be biochemical.
Note: At first, you may not know if your rock is crystalline or just composed of very small particles. You may need to review both tables to determine your rock name.
Second, use Tables 1 and 2 in the SEDIMENTARY ROCK NAMING CHART to find the name for your rock.
COLUMN 1: Composition. Determine the composition of your rock. What is the dominate grain size of your rock? What is the mineral composition of the grains? What about the composition of the matrix?
COLUMN 2: Texture and Description. Is the rock sample composed of various different rock and mineral fragments or single mineral? What is the size, rounding, and sorting of the fragments within the rock. Are there any visible sedimentary structures? Are there any visible fossils? Does the rock sample react with HCl?
Third, enter your notes for each rock sample in the Sedimentary Rock Characteristics Fill-In Table below:
COLUMN 3: Rock Name. Compare your observations of rock texture and composition to the descriptions given in the lab, then determine a rock name using COLUMN 3 from Tables 1 and 2.
COLUMN 4: Depositional Environment. Examine the rock and select the best environment that you think it reflects.
If you are looking for additional resources to help with rock identification, I have additional posted videos here.
Problem 2:
Review the images below and answer the following questions regarding the sands. Each photograph of sand grains below was taken at 20X power. (Pictures are in the files for this problem) The field of view represented is approximately 3 mm across.
Enter your answers in the text field below. Please also copy-and-paste the questions into the text field so that it is clear which questions you are answering.
A) Olivine Sand:
This olivine sand is from the famous green beach from near the southern tip of the island of Hawaii. What is a plausible source of the olivine sand given what you know about Hawaii?
B) Oolitic Sand:
Although these sand grains are round they are not rounded from transport. Rather, they are examples of hydrogenous sediments, comprised of the mineral calcite (CaCO3). In what type of general environment might you find these oolitic sand grains?
C) California Beach Sand:
This typical California wave-washed beach sand rich in quartz, which looks a bit like bits of glass under magnification. Assume the beach sand was sampled from Long Beach and is derived from rocks in the San Gabriel Mountains. Describe a plausible history of the beach sand. Start with weathering of the rocks in the San Gabriel Mountains. Consider which transporting agent(s) may have delivered the sediment to the ocean. Make sure to address changes to clast size and rounding that are likely to occur on such a journey.
D) Aeolian Sands:
Aeolus in Greek mythology was the keeper of the winds. As such, the term “Aeolian” or “Eolian” means “wind-blown.” When sand grains are wind-blown, they bounce along the surface of the earth in a process called saltation. What effect does wind have on the sand grains? Your hint is to compare this sand in composition, rounding, and appearance with the CA Beach Sand above.
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