Sunday, February 19, 2012

This week my class will be joining me in the cemetery for a fieldtrip. As we live in an urban area it is difficult to get out and look at rocks, but there is a cemetery very close to campus. Cemeteries are very good places to assess the weathering of different rock types as well as we know when the headstone was erected giving us an idea of how the rocks are weathering over time.

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





3 - Weathered but readable





4 - Heavily weathered, barely readable

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