Logging Requirements
1. Take a look at the various layers. Do you see any breaks, waves, or changes in the patterns that suggest additional stresses on this rock after formation? If you do see patterns suggesting this, please describe what you see that leads you to this conclusion.
2. If you had to guess, how many layers are present in a one-inch cross section of this specimen?
3. (optional) Take a picture with the rock and your team and/or GPSr at the rock.
4. Extra credit- Where was this rock located prior to its current location?
Why the nice layers?
The layers are what make Gneiss nice. They are formed by what geologists term a directed stress field. That is, as rocks are pushed together under great heat and/or pressure, the minerals tend to react to the greatest degree of compression by flattening perpendicularly.
Set in Stone...
The term "set in stone" only partially applies in this situation. Once the rock has formed, forces can still act on it. If there are additional stress events after these rocks have formed, it may be shown as waves, breaks, or other interesting non-linear layers.
How did it get here?
This rock didn’t form in Ann Arbor. It was deposited here during the last ice age (14,000-18,000 years ago) as a very early Canadian export. Glaciers dropped this specimen here as one of the first patrons of the (now) parking structure.
What is it used for?
Besides earthcaches, gneiss is utilized for flooring, gravestones, building facing, and monuments (e.g., one of the components in the Washington Monument is gneiss).
Sources
http://geology.com/rocks/gneiss.shtml
http://csmres.jmu.edu/geollab/Fichter/MetaRx/index.html
http://www.nps.gov/nr/travel/wash/dc72.htm