You are standing in front of the six story "skyscrapper" of downtwon West Chester. It was built in 1908. The exterior is faced in Indiana limestone and yellow hard face brick. You are here to learn about limestone and weathering on limestone.
Though not exactly necessary, a magnifying glass might be useful in examining the limestone and it's components..
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.
Weathering
These things made serpentine a popular building material, but becasue sandstone easily crumbles, the rock is very vulnerable to weathering: Chemical Weathering, Biological Weathering, and Mechanical Weathering.
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Chemical weathering
This occurs when minerals in rocks are unstable in their environment and can be altered or dissolved. Rainwater, which contains a weak carbonic acid, reacts with limestone. Carbon dioxide from the air or soil sometimes combines with water in a process called carbonation. This produces a weak acid, called carbonic acid, that can dissolve rock. Carbonic acid is especially effective at dissolving limestone. Different chemicals in the air can erode substances like the serpentine rock or the copper crown on buildings. Airborne sulfer, carbon dioxide and oxygen can all erode substances. Chemical erosion occurs when a rock's chemical composition changes, such as when iron rusts or when limestone dissolves due to carbonation.This building shows several areas of chemical erosion. One of the greatest examples of chemical erosion on copper is the Statue of Liberty. She was one a shiny orange statue which has oxidized over the years to the green statue we know.
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Biological weathering
This occurs when living organisms, like plants and animals, cause rocks to break apart. Plants cause weathering by taking root, causing cracks and crevices in objects.
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Mechanical weathering
This occurs when rocks break into smaller pieces without changing their chemical composition. For example, water can seep into cracks in rocks, freeze, and then thaw, causing the rocks to break away. The removal of soil, rock particles, and other materials by the flow of water is mechanical weathering. Day time temperatures can heat and expand the limestone, and cool night temperatures can shrink and contract the limestone causing mechanical weathering. Over years, human interaction with rocks can weather them. Even walking on the same patch of rock over time can gradually wear it down
Questions to Answer:
Please send me the answers- do not include them in your log.
In order to get credit for this earthcache you need to do the following.
1. Describe the overall color and texture of the limestone at this site. Rough or Smooth? Buff, Grey, or Variegated?
2. Go to the Northeast facing corner of the building. On this side there is a particular slab that has some interesting characteristics and weathering. Describe what you see here and how this might inform you as to where this rock was formed?
3. Take a picture of an example of weathering, label it and send it in your message to me, don't include it in your log.
Optional: Post a picture of yourself or your GPSr or other personal geocaching item at the building in your log.
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
How does weathering affect limestone https://www.internetgeography.net/topics/how-does-weathering-affect-limestone/#:~:text=Weathering%20is%20the%20breakdown%20of,causes%20the%20limestone%20to%20dissolve.
Farmers and Mechanics Building https://en.wikipedia.org/wiki/Farmers_and_Mechanics_Building