The Geology of Rushmore

Well it just would not be right to go to Mount Rushmore without some geology pictures and discussion. Picture 1 shows a close up of the pegmatitic veins and pockets that can be found within the granite that makes up Mount Rushmore. I have a picture of Lincoln with a pegmatic vein around his head and one that cuts across his face just above the left eye, it resembles a scare such as Andrew Jackson. You can see gray quartz in the center of the picture and to the left. The quartz is surrounded by large mega crystals of potasium feldspar (oligoclase) with perthitic texture. I brought some samples home in case you want to see it. The crystals are large 4-6 inches. Not a very pretty color but the crystal shape is mostly complete and it is a good specimen. There are also books of muscovite mica that are also in the picture. I need to play with the photo on photoshop to enhance the picture so you can see all of these minerals clearly.

Picture #2 shows the relationship of the granite intrusion to the Precambrian mica schist. The intrusion when it intruded the schist deformed it as you can see in the photo (again, I need to enhance this picture). You can see the curved bed of the schist and the granite surrounding it. The schist looks like a tree root, but it isn't. Also you can see where groundwater has flowed along a fracture in the granite and altered the feldspars to clay. I have another fine picture if you would like to see it. Just ask me and I will email it to you.

Picture #3 shows the actual granite that the presidents are carved in. I believe it is anyway. These polished slabs of granite line the walk way that leads toward the view of the carvings. In the walk way are 15-20 posts that are also tiles with the granite. Each post has four state flags one flag on each side of the post, and below each state flag is a granite slab with the name of the state carved into and the year it became a state. I took pictures of each of the states and their respective flags that are important to our family: Wisconsin, Colorado, and Utah. Nobody lives in California yet so I didn't take a picture of it. If anybody is sad about that I can go get a picture of it another day. The granite may not be actual granite from the mountain but it is very nice and it looks like it came from the rubble on the talus slope. You will notice the biotite and pink feldspars and gray quartz.