MN DNR Minerals Education Workshop 2005
Field Trip guide by Dr. Dean Moosavi and Rick Ruhanen
|A limestone quarry. Limestone is a mixture of mostly 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 would be subjected to more pressure and heat it would turn into marble.
This stone was formed during the Ordovician period of geologic time. They are 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 of a large shallow sea covering this part of Minnesota. Also present are fossils of stromatolites, gastropods, cephalopods, pelecypods, crinoids and a few brachiopods and trilobites.
Here the limestone is being quarried (mined) for building stone and decorative stone. The loose top rocks and dirt are first pushed away then a diamond tip saw looking much like a very large chain saw cuts into the stone at intervals of about 2 meters. This type of rock is common in southern Minnesota but is economical to mine here because the Minnesota River (Glacial River Warren) eroded the material over the top of the stone bringing it near the surface for easy access.
|After the saw is done a drill is used to put in a series of holes along which the stone will break. When the stone is ready to be removed from the quarry an operator uses a air powered wedge to connect the drill holes with a crack in the stone. In the photo below the drill holes are visible as vertical slots in the side of the stone. A loader then pushes the stone out of its bed and loads it for transport.
A block of stone has six sides, two are cut by the diamond chain saw, two are cut by drilling holes to cause a weakness for a crack to follow. The top and bottom are natural breaks in the stone layers of sand or shale (compacted mud). The thickness of the quarried stone depends on the these natural breaks and makes it easier to quarry.
|The stone is brought in large blocks to this saw where it is cut into slabs from 3/4 to 6 inches in thickness. The stone is then sorted and graded before being further macined. The stone can have many uses for building and decorative uses. In the photo at the bottom right workers are grinding the stone into parking lot barriers. Some of the slabs are used to cover the outsides of buildings, like many of the buildings at Minnesota State University in Mankato. The stone is a long lasting, maintanence free material.|