Elephant Rocks State Park
Elephant Rocks State Park is the smallest of the state parks we visit, the trail which forms the circumference of the park is only about 1.5 km long. The park contains, however, exposures of some of the more beautiful granite that I have seen. I was first introduced to this rock when I came down to Washington University in St. Louis. The older buildings on campus are all wonderfully faced with the Graniteville Granite, which is the rock exposed here in the park. Indeed, the trip through the park includes walks by a set of old quarries. The image on the right shows the students walking through the first (and most recent) of the quarries.
From left to right the students looking at the Graniteville granite in this quarry are Stuart Perez, Michelle Platt, and Aimee Forgey. The blocks left behind can be several meters in length, as those present in the image on the right where Stuart Perez stands among these looking at the mineralogy of the granite. Most of the granite seen in the park has mineralogy as described by Kisvarsanyi and Hebrank (1987). The Graniteville granite is a medium- to coarse-grained alkali granite. The average composition of the granite includes orthoclase feldspar (55%), quartz (40%...that's a lot of quartz!...) and less than 5% mafic minerals. Some evidence of basaltic intrusions are visible however.
The image on the left shows a piece of rock in the quarry (and therefore not found in situ) which exhibits half Graniteville Granite and half a mafic intrusion with many phenocrysts of potassium feldspar in it.
The Graniteville granite is know commercially as a "Missouri Red" monument stone. It has been quarried since 1869. The Graniteville Granite has been used as paving stones, monument stones or facing stone in nearby St. Louis, as well as far to the east in Pittsfield, MA and as far west as San Francisco, CA.
The Elephant Rocks State Park forms a geomorphic province called a tor. A tor is a high, isolated rocky peak, much-jointed and usually granitic, exposed to intense weathering and often assuming peculiar or fantastic shapes. The fantastic shapes
associated with Elephant Rocks comes from chemical weathering along joints that developed in the granite by magma cooling and by the release of the overlying burden when erosion and uplift brought the granite to the surface. The weathering process removes layer after layer of the granite. The process is referred to as exfoliation, and the image to the right shows the weathering process exploiting a fracture on the surface of the large granite surface directly beneath the "elephants". The net result of this weathering is shown in the following two images. Both of these include the same students (identified in the left image, from left to right, Stephanie Carter, Amanda Riebel, Duane Ford, and Michelle Platt). In the image on the left, you can get some feel for the size of the granitic boulders formed by this slow process of chemical weathering.
The image on the right allows you to look out over the southern St. Francois Mountains from a vantage point atop the granitic tor. In the rocks atop the tor are also carved names and initials of the some of the master carvers from the quarries that we had come through to reach this point. The students also made some quick, back of the envelope calculations on the weight of these blocks by estimating their hypothetical radius, calculating a volume an using a typical density for granite of 2700 kg/cubic meter.
Alas, the visit to the Elephant Rocks State Park was not without a small share of turmoil.
As we see in the image on the right, upon learning that Duane Ford had eaten all of the communal cookies without asking permission, he was assigned a somewhat Sisyphean task.
Kisvarsanyi, E. B. and A. W. Herbank, 1987. Elephant Rocks: A granite tor in Precambrian Graniteville Granite, the St. Francois Mountains, Missouri, in D.L. Biggs, ed., Centennial Field Guide, Volume 3, Geological Society of America, 159-160.
To learn more about Elephant Rocks State Park, check out the park pamphlet by clicking on the icon to the left. Inside this site is a link to the Missouri Department of Natural Resources
web page for the park.
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Elephant Rocks State Park is the smallest of the state parks we visit, the trail which forms the circumference of the park is only about 1.5 km long. The park contains, however, exposures of some of the more beautiful granite that I have seen. I was first introduced to this rock when I came down to Washington University in St. Louis. The older buildings on campus are all wonderfully faced with the Graniteville Granite, which is the rock exposed here in the park. Indeed, the trip through the park includes walks by a set of old quarries. The image on the right shows the students walking through the first (and most recent) of the quarries.
From left to right the students looking at the Graniteville granite in this quarry are Stuart Perez, Michelle Platt, and Aimee Forgey. The blocks left behind can be several meters in length, as those present in the image on the right where Stuart Perez stands among these looking at the mineralogy of the granite. Most of the granite seen in the park has mineralogy as described by Kisvarsanyi and Hebrank (1987). The Graniteville granite is a medium- to coarse-grained alkali granite. The average composition of the granite includes orthoclase feldspar (55%), quartz (40%...that's a lot of quartz!...) and less than 5% mafic minerals. Some evidence of basaltic intrusions are visible however.
The image on the left shows a piece of rock in the quarry (and therefore not found in situ) which exhibits half Graniteville Granite and half a mafic intrusion with many phenocrysts of potassium feldspar in it.
