When looking at a headstone we must make some observations. The first will be the composition of the headstone. The headstones in Evergreen Cemetery are composed of one of three rock types: igneous, sedimentary, or metamorphic.
The igneous headstones are composed of granite. Granite is an intrusive igneous rock so it is coarse-grained meaning the individual crystals can be seen with the naked eye. It has a crystalline texture which gives it a speckled appearance. Granite is often pink, black and white or white and black. Granite is quite resistant to weathering. Below is a photo of a granite headstone:
Next we have a close-up of a pinkish granite:
Now a close-up of a white and black granite:
The sedimentary rock most commonly used for headstones in Evergreen Cemetery is limestone. This rock is a biochemical sedimentary rock and it often appears to be made of shells and sand grains glued together. This limestone is a buff color and can also be seen in the columns of the KOM building. Stop and take a look the next time you're heading to class. Limestone weathers very easily and therefore is not used for headstones very often.
See below for photos of two limestone headstones. Note the weathered appearance of these headstones:
Headstones for Woodsmen of the World are often shaped liked trees and are made of limestone:
Next we have a close-up of limestone showing the shells and sand grains glued together:
The third rock type used for headstones is marble, a metamorphic rock. Marble is a non-foliated rock created by the metamorphism of limestone. Marble is soft and is often used in sculptures. It is often white in color and has a sugary appearance and it can be covered in lichen. Marble weathers easily and many old marble headstones are now illegible.
Below is a photo of a typical marble headstone, including lichen covering much of the headstone:
Next is a close-up of a marble headstone:
After determining the type of the rock used for the headstone we must then assess how weathered the headstone is. We use a scale to assess weathering and below are examples of each step on the scale:
1 - No indication of weathering
2 - Some weathering, but easily readable
Friday, February 3, 2012
Plate Tectonics Vacation Snaps
I don't really have any specific plate tectonics photos, but these two can be related to plate tectonics.
This photo was taken in Iceland. Iceland is located on a hotspot and on the Mid-Atlantic Ridge. I went on a research cruise that departed from Reykjavik. You can go see the Mid-Atlantic Ridge as a surface feature in Iceland. Unfortunately I was not able to do that as we had only one night in Iceland before the cruise left.
This photo was taken in Great Smoky Mountains National Park. This park is part of the Appalachian Mountain chain, which formed when the supercontinent of Pangaea was assembling in the Paleozoic.
This photo was taken in Iceland. Iceland is located on a hotspot and on the Mid-Atlantic Ridge. I went on a research cruise that departed from Reykjavik. You can go see the Mid-Atlantic Ridge as a surface feature in Iceland. Unfortunately I was not able to do that as we had only one night in Iceland before the cruise left.
This photo was taken in Great Smoky Mountains National Park. This park is part of the Appalachian Mountain chain, which formed when the supercontinent of Pangaea was assembling in the Paleozoic.
Plate Tectonics
This week in class we've been talking about plate tectonics. We started by discussing Alfred Wegener and his theory of continental drift. My personal blog is called Continental Drift and I have a "Stop Continental Drift" bumper sticker on my car so I'm a big fan of Wegener. He was a man ahead of his time and didn't live to see the acceptance of his theory. You can read about the reactions to his theory here and here. One of the important advocates of continental drift and plate tectonics was an Australia geologist, Samuel Warren Carey.
After continental drift we discussed seafloor spreading, proposed by Harry Hess. As Callan Bentley writes continental drift + seafloor spreading = plate tectonics. We have only just started discussing plate tectonics in class and talked about the lithosphere and the asthenosphere and divergent plate boundaries today. You can see some animations of plate tectonics, including divergent boundaries, here and here.
There is an interesting blog about using diamonds to date the start of plate tectonics. The isotopic dating of diamonds with eclogitic inclusions, which might be formed from partial melting during the formation of the coeanic crust, shows that plate tectonics may have started around 3 billion years ago.
I also found an interesting series of blogs about subduction denialism written by Brian Romans. You can read these posts here: part 1, part 2, and part3. I never knew there was such a thing as subduction denialism and they tie it in with the expanding earth theory. Part 2 of that series of posts has excellent topographic profiles of various subduction zones/deep ocean trenches.
After continental drift we discussed seafloor spreading, proposed by Harry Hess. As Callan Bentley writes continental drift + seafloor spreading = plate tectonics. We have only just started discussing plate tectonics in class and talked about the lithosphere and the asthenosphere and divergent plate boundaries today. You can see some animations of plate tectonics, including divergent boundaries, here and here.
There is an interesting blog about using diamonds to date the start of plate tectonics. The isotopic dating of diamonds with eclogitic inclusions, which might be formed from partial melting during the formation of the coeanic crust, shows that plate tectonics may have started around 3 billion years ago.
I also found an interesting series of blogs about subduction denialism written by Brian Romans. You can read these posts here: part 1, part 2, and part3. I never knew there was such a thing as subduction denialism and they tie it in with the expanding earth theory. Part 2 of that series of posts has excellent topographic profiles of various subduction zones/deep ocean trenches.
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