Enchanted Rock

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Enchanted Rock Enchanted Rock is located near Fredericksburg Texas. It is a granite rock that rises 130m (425 ft) to the top, 1825 feet above sea level, and covers 640 acres. At the base there is a dry creek bed of granite that has been cut by a series of fractures. Fine black rock along these fractures is called gouge. Fault gouge is comprised of little pieces of rock that was ground upward when the fault moved. Once you go up the trail and climb past the trees to the large space of bare rock, you are on the exfoliation dome. At this point you can examine the “coarse-grained porphyritic granite that makes up the majority of Enchanted Rock”. As you examine the surface, you will see how the granite magma cut into the surrounding rocks. When this occurred over a billion years ago, the magma was a combination of very hot liquid and crystals. Once you reach the mid-point of the climb you can see to your right a boulder-covered granite hill known as “castle tor”. An area on the rock that looks like a line down the slope is called an aplite dike. Several of these cut the rock; these consist of fine-grained granite with a sugary texture and minimal biotite. Dike describes the crack where molten rock has been inserted. As you climb up the front, a section of rock has a texture change. This appears to be a Ductile Shear Zone, a long narrow change that has a more fine grain consistency. From the top of the rock you can see gnamma pits. These are areas where the rock has weathered, leaving pits in the tock that soil builds into and plants hold it in place. The deeper the pit and soil, the larger the plants can grow. From the top of the rock looking north, you can see a line of pink hills or small castle tors. Looking to the east you notice a flat topped hill, this is the Edwards Plateau. This is composed of limestone, which at one time covered the top of Enchanted Rock but eroded back, exposing the granite. Our tour now heads downward and we pass a weathering characteristic that looks like a doughnut ring with a gnamma pit in the center. Along the decent we come across a Tent Blister, a sheet of rock that breaks in the middle and the center portion of the rock elevates into a point.
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