Meta Rocks Hill Country
What exactly are metamorphic rocks? Well, these types of rocks arise or transform from other existing rocks to form what you may see here at GZ and the surrounding area. The forming of new rocks is a process called metamorphism. Whatever the original rock was at one time or another submitted to certain temperatures which often changed the pressure of the rocks causing the change in composition of the rocks and therefor forming them into what you may see today.
So the next question that should be asked is are these rock types found here in the Texas Hill Country? The answer would be yes. But why? That would be because the Texas Hill Country area originated before the age of dinosaurs which make the area unique compared to other areas in the state. Since the formation times, this unique landscape has gone through a myriad of changes. These changes serve to give the area its distinctive and beautiful scenic views you experience today. It would be surprising to most that the Texas Hill Country was once an area with volcanoes that spouted their lava over the area which you see today. Pilot Knob was an area created by volcanic surges.
What are some of the characteristics of metamorphic rocks that separate them from other types of rocks you may ask. Well, metamorphic rocks are usually more coarse than other type of rocks. Grain coarsening is usually the result of the metamorphism process mentioned above. There are numerous examples of metamorphic rocks. Some examples are gneiss, marble, slate, schist, and quartzite. In addition to these examples of metamorphic rocks, there are also different types of minerals found within these rocks. Those include sillimanite, kyanite, staurolite, andalusite, and some garnet.
Questions and Tasks
1. At and around GZ you will find some very large samples of metamorphic rocks. Based on your reading above, please describe the type of rock you see. In addition what type of minerals if any can you spot?
2. What type, color, and texture rock did you find these in?
3. In what looks like a washout of ditch that runs parallel to the road at GZ do you see any smaller metamorphic rocks? Why or how do you believe this is formed this way?
4. As proof that you were at the location of this earthcache, please post a picture of yourself and/or your group or a picture of your GPS or phone at this location.