Questions to Answer:
Please email the CO with these answers- do not include in your log.
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Describe the overall color and texture of the limestone at this site. Rough or Smooth? Buff, Grey, or Variegated?
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Go to the Southeast corner of the tower. On the south-facing side is a particular slab that has some interesting characteristics. Describe what you see here and how this might inform you as to where this rock was formed?
What is Limestone?
Limestone is classified as a type of sedimentary rock, meaning the formation of these rocks depends on layers upon layers of sediment hardening over time. Sedimentary rocks are typically classified into three basic types:
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Clastic: Rocks made up of other rocks that have been compacted together and/or cemented together by a mineral. One such example is sandstone.
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Chemical: Rocks formed from dissolved minerals that are precipitated from solution. Examples include rock salt and certain kinds of stalagmites (in caves).
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Organic: Rocks created from the bodies and waste byproducts of living organisms. Examples include coal and limestone. Marine fossils can be found in organically-formed sedimentary rocks.
How Organic Limestone is formed
As the diagram illustrates, sediment is deposited on the ocean floor from dying plant and animal life,along with any airborne or ground-borne debris. The weight of subsequent (newer) layers of sediment compacts the lower (older ) layers into rock. Some skeletal remains typically survive this process as fossils, hence much of this rock consists of calcium carbonate.
Origin of this Limestone
The organic limestone at this earthcache was formed in a shallow parts of an inland sea during the Mississippian Period (330-360 million years ago) in an area now known as the State of Indiana. Also known as Indiana Limestone, this rock was mined in south central Indiana (close to Indiana University-Bloomington). There are three basic iterations of this region’s limestone: buff, grey, and variegated (combination of buff and grey).
Why is this limestone here?
This particular structure was erected in 1935-36 as a memorial to a former president of the University of Michigan, Marion Burton.
Limestone was a popular upscale building material in the 18th and early 19th century (prior to the advent of acidic rain, which doesn’t play well with calcium carbonite). Indiana limestone, in particular, has some added building material benefits. According to the Indiana Geological Survey, this region’s rock can be classified as a freestone because “it exhibits no preferential direction of splitting and can, therefore, be cut and carved in an almost limitless variety of shapes and sizes. This property allows the stone to be planed, turned on a lathe, sawed, and hand worked to match the requirements of the most demanding architectural designs.”
A number of notable structures have been built with Indiana limestone, including the Pentagon, the Empire State Building, the new Yankees Stadium, and the National Cathedral in Washington, DC.
Sources
Arizona State University: http://ratw.asu.edu/aboutrocks_sedimentary.html
University of Cambridge : http://www.thenakedscientists.com/HTML/questions/question/2006/
Indiana Geological Survey: http://igs.indiana.edu/MineralResources/Limestone.cfm
University of Michigan, History of Burton Memorial Tower: http://umhistory.dc.umich.edu/mort/central/north%20of%20north%20u/Burton%20Tower/index.html
congrats HelloLola, FTF