For our last Geology class we covered the last major type of rock, Metamorphic Rock, and then learned a little bit about our local North Carolina Geology. I also asked them to bring in a favorite rock of their own to share. We ended up spending a great deal of time looking at and talking about the rocks they brought in... more than I had planned for, so we didn't get to the final video (Bill Nye: Rocks and Soil).
Metamorphic rocks are rocks that have been changed by pressure and/or heat. There are two kinds of metamorphic rock, those that formed in a volcano or around a magma chamber (contact metamorphism), and those that formed by heating and pressure deep underground, usually during mountain building or along tectonic plate boundaries (regional metamorphism). There is a third and very rare form that happens when lightening strikes or a meteorite hits, called shock metamorphism. Shock metamorphism can produce things called fulgurites from melted sand.
Metamorphic rocks tend to be very hard, because the pressure and heat compacts the atoms and molecules (minerals) together. Some of the hardest is a rock called gneiss (pronounced "nice"). The color of this rock depends on what minerals are in it. Most of the worlds major mountains are made up of metamorphic rock.
Here are some examples (I tried to have some actual examples of each):
shale ----> slate ------> phyllite (Slate is used for black boards and roofing tiles.)
limestone ----> marble (The most widely used of rocks. The Lincoln Memorial, the Washington Monument, The Parthenon, and the Taj Mahal are all made out of marble.)
Mudstone -----> schists
quartzite (Used for road building and millstones.)
My naturalist friend had given me a bunch of rocks she had collected in a local stream. These were probably schist, but they had a great deal of mica in them as well as garnets. The garnets, a semi-precious stone, looked like little black balls in the rock. Formed in metamorphic rocks, it was a wonderful way to explore something local, get an idea of how unimpressive most precious and semi-precious stones look before polishing, AND they got to keep them!
North Carolina has a very complex and old geologic history. It has been formed over the Eras from a series of tectonic plate collisions and separations. The Appalachian Mountains were formed over 220 million years ago when parts of Africa and South America collided with North America. They probably topped 20,000 feet or higher, rivaling the Himalayas of today. At that point, North Carolina was on the edge of the tectonic plate and volcanically active. Since then the Atlantic Ocean has been spreading, putting down crust and moving the region to an inactive central position. The mountains have also been eroding over this time (Blue Ridge province), helping to form the Piedmont and Coastal Plain provinces of the state. The Coastal Plain is currently under 1,000s of feet of sediments from the Blue Ridge mountains. The Blue Ridge is still the highest of the Appalachian chain with 43 peaks over 6,000 feet tall.
I fortunately had access to a large map print out of North Carolina geology. It was more complicated than I needed, but it was great to be able to spread it out and look it over as I talked. A great resource for North Carolina maps and other geological information can be found at the North Carolina Geological Survey: http://www.geology.enr.state.nc.us/answers.htm
Some fast facts about North Carolina Geology:
*The State rock is granite.
*The State mineral (precious stone) is the emerald.
*North Carolina was the first place in the United States where gold was found.
*The oldest rocks we have found in this state were dated to 1800 million years ago and were found at Roan Mountain.
A wonderful book for exploring North Carolina Geology is Exploring the Geology of the Carolinas: A Field Guide to Favorite Places from Chimney Rock to Charleston by Kevin G. Stewart and Mary-Russell Roberson. In it are some great field trip ideas as well.
I finished up our class with a little quiz game of my own devising. They made teams and built a volcano by answering questions correctly. The first to "erupt" their volcano won. This was pretty simple to put together and got the job done as far as trying to get them to review what we covered.
There are many topics I did not cover in my class: caves, crystals, how to tell if you have a certain type of rock, mountains of the world, soils, oil and gas exploration... the list goes on. I only had five days though, so I think we covered a good portion of the basic material.
I did just dig up (Ha!) one final resource on basic geology at Robert Krampf's website. I love him for fun random videos on all things science. This is a nice simple lesson plan: http://thehappyscientist.com/study-unit/rocks. I'm not sure if you need to be a member to view this, but even if you can't see it, check out his free videos. They can be a lot of fun.