The blocks that cover the exterior of this wall are made of limestone. The limestone came from a quarry in Mankato, Minnesota. Due to erosion caused by the nearby Minnesota River, the limestone formations in this area are close to the surface, which allows relatively easy access for mining. There are limestone blocks used throughout this building totaling 100,000 square feet.
Limestone is a mixture of shells from sea creatures (clams, snails, etc) and clay. It is compacted under layers of water, rock and earth until it forms a sturdy rock. If the limestone had been subjected to more pressure and heat, it would have turn into marble. This stone was formed during the Ordovician period of geologic time. The formation is part of what is called the Prairie du Chien group (after the town in western Wisconsin) and are divided into Oneota and Shakopee Formations. The stones themselves are evidence that a large shallow sea covered this part of Minnesota.
In order to count this Earthcache as a find, you must locate the piece of limestone on the wall that has a 2010 LEED SILVER plaque on it, complete the following tasks and email the answers to me.
1. Describe the piece of rock with the plaque on it. What colors do you see in the block of limestone?
2. Do you think it is in the same orientation that it was when it was under the sea? Why or why not?
3. Measure the height, width and estimate the thickness of the block in inches. To estimate the thickness of the block, look at the blocks in the nearby doorway. If limestone has a density of 0.06 pounds per cubic inch, how much does this block weigh (weight = height X width X thickness X density)?
Resources:
Minnesota Geology Field Trip, Summer 2000 and Other MN DNR Workshops Arlyn DeBruyckere with Dr. Tim Kroeger and Dr. John Annexstad Bemidji State University
Photos of this piece of limestone will be deleted if posted.
After sending the answer, go ahead and log your find. No need to wait for a response.