From The Rock-N-Rose Newsletter ETGMS, May 2007
Llano Field Trip, April 28-29, 2007
A 7-car caravan of East Texas rockhounds snaked through the hill country recently, going home several pounds heavier (with rock!) and some good memories. I cannot quote the officially stated purpose of the East Texas Gem & Mineral Society but I feel sure that goal was achieved on this particular trip. Carefully planned stops with accompanying geologic information on each site yielded cherished specimens collected with friends on a beautiful day midst colorful hill country flowers. Don, The Man, led us not astray, but on an adventure where thirteen members joined in picking up and packing up town mountain granite, very nice gneiss, hematitic sandstone, wonderful surreptitiously-collected serpentine, amphibolite, salvaged marble scraps and, of course, llanite! Now we all understand why a good hat and a blade chisel are essential tools and that bringing food to share makes lunch fun. It was an exhausting but exciting two days of successful rock-hounding,
~ Becky Whisenant ~
Now the Rest of the Story
The second day of our geology field trip in the Llano, Texas area started early with a drive to the scenic overlook at Hoover’s Point just south of Kingsland. Hoover’s point is one of the most beautiful spots in central Texas overlooking Lake LBJ. It alone is worth a stop. But we were there to look at the huge road cut comprised of Cambrian rocks of which the large hill is composed. The Cambrian rocks are approx. 550 million years old.
The main item of interest at Hoover’s Point is the bright grass green to blue green glauconitic sandstone. The mineral glauconite gives the sandstone both its green coloration and name. Also encased in the layers of green sandstone are small lenses of trilobite coquina limestone. Coquina is a term used to describe a limestone made up of broken fossil shell fragments. Club members were able to pick up arm loads of each type of material, and dodging a few speeding cars and trucks made our way safely back across the busy highway.
Our next stop was a few miles northwest of Kingsland on the back side of Packsaddle Mountain on Highway 71. We stopped at a road cut just north of the Honey creek crossing and looked at the metamorphic Packsaddle schist. There we collected hornblende and graphite schist. Cutting through the schist layers is a small pegmatite dike, and club members collected some pieces of quartz and feldspar. The packsaddle schist was originally marine sedimentary rocks which have been metamorphosed into schist. The Precambrian Packsaddle schist is approx. 1.25 billion years old, and is the second oldest rock formation found in the Llano uplift area.
The third stop of the day was a few miles south of the Hwy 71 side on a dirt county road where we collected micro sized crystals of tourmaline and hornblende. We also found larger pieces of massive hornblende. The micro tourmaline and hornblende crystals occur in the contact between small thin quartz veins which run through the surrounding shinny light golden colored mica schist. The mica schist is a part of the Packsaddle schist. Jack Shull and I have been examining our micro specimens under microscopes since we returned from Llano, and have discovered small wine colored garnets occurring with the tourmaline and hornblende in the mica schist. So if you went on the trip and collected some of the material, you may want to re-examine your specimens through a hand lens looking for small garnets.
At the next couple of sites we collected actinolite schist from a road site county rock pit. The actinolite schist is light green in coloration and quite shiny. Next we collected quartzite/leptite, which is a feldspar rich metamorphic sandstone. This we found at the Sandy creek crossing a few miles south of the abandoned community of Click. Further down the road, we collected more metamorphic rocks like orthoamphibolite which is metamorphic gabbro/basalt. The orthoamphibolite is dark green with white splotches and polishes into a pretty stone. It is composed of hornblende and plagioclase feldspar. Next, just on the edge of Click, we collected soft black graphite schist in the road bed. The county used the graphite schist as road material. All of the rocks we collected in this general area were from the Packsaddle schist formation. After collecting in Click, we made or way north to a country cemetery to have lunch. No, we didn’t eat in the cemetery, nor did we collect rock s in the cemetery. There was a nice spot out side of the cemetery with grass and trees to sit under and enjoy our lunch and listen to Marilyn Austin and Gene Goar banter back and forth to our amazement and amusement. After lunch we made our way to the last stop of the day were we collected some mica schist, and marble. Before we left the spot, I made my way off into the brush to take care of some personal business and upon completion of that task, making my way back to the truck I tripped over a chunk of Llanite. What!!! Llanite approx. 25 miles from where we had collected llanite the day before. Who knows? At that point we headed home with a truck full of rock, and wondering who threw that chunk of llanite out into the brush.
~ Don Campbell ~