Milbank Granite EarthCache
-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. Describe the area at ground zero.
2. Describe the texture of the granite.
3. Describe the color of the granite. What does this tell you about the amount of feldspar present?
4. Look at the crystals in the granite. What do they look like? What color are they? How big are they?
5. Describe the scrap mounds in the area.
This Earthcache is located in the Robert Hunter Memorial Area near Milbank, South Dakota. This public water access area, which is really a water hole surrounded by granite. One can fish or swim in the waters or just enjoy the granite-filled area. The Dakota Granite Company has granite quarries just to the east and south of this location. Surrounding this area, one can see large mounds of imperfect stone and waste rock that have become part of the landscape. Enjoy!
At an age of about 2.5 billion years, the Milbank Granite lies beneath about thirty square miles of land in northeastern Grant County--just east of the town of Milbank.
Granite is an igneous rock. Igneous rock is formed when hot magma or lava cools. This type of rock can occur in one of two forms: intrusive or extrusive. Volcanic rocks (rocks that exit volcanoes in a liquid state and cool to solidify at the Earth’s surface) are extrusive rocks. These rocks come out of the Earth--they are extruded from the earth.
Granite is an intrusive rock; it forms far beneath the earth’s surface. Beneath the surface, magma is slowly pushed up from the core of the earth. It fills any crack or space it can find, sometimes pushing other rocks out of its way on the subsurface. This process can take millions of years to complete. During this time, the rock slowly cools and solidifies into a hard rock. Many mountain ranges throughout the world are formed by this kind of intrusive rock.
Granite is made of crystals. These crystals can easily be seen with the naked eye, unlike lava rocks. Even though lava rocks and granite are made essentially through the same process, speed is the important factor here. In lava rocks, the crystals are too tiny to be seen with the naked eye because the rock cooled too quickly for the crystals to grow large. Granite, on the other hand, cooled slowly underground. The rock surrounding it shielded the granite and allowed the heat to escape slowly. This gave the crystals time to grow.
Granite is also comprised of feldspar, quartz, and small traces of other minerals. The feldspar and quartz give granite its texture. The distinct pink color of the granite is due to the alkali feldspar. The Milbank Granite consists of about sixty percent dark red feldspar, twenty-five percent clear quartz, and fifteen percent black biotite mica.
The first commercial stone quarry in this area opened in 1908. Since then, the number of active quarries has varied from one to eight. The granite quarried in different areas have varied in color and have led to many trade names: Mahogany Granite, American Rose, and Royal Purple. The color variation depends on the amount of feldspar present in the granite outcropping.
Milbank Granite is also special in that it contains the fossil remains of several species of sharks, sea turtles, and fish that thrived in the area about 65 million years ago when the inland sea advanced far enough east to cover the area. During this time, sandy shale was deposited on top of the granite. Although most of the shale was later eroded, small pockets of shale have been preserved between the granite knobs. It is here that the fossils can be found.
Granite is widely used throughout the state (and region) as building stone. The rock takes a high polish and is largely used as a facing on the lower portion of buildings, as interior trims, and as tombstones. Milbank Granite can be seen in the large stairway in front of the state capitol at Pierre and in the large columns in the National Catholic Shrine in Washington, DC.
NOT A LOGGING REQUIREMENT: Feel free to post pictures of your group at the area or the area itself - I love looking at the pictures.
Additional Hints
(No hints available.)
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
Loading Treasures