Category Archives: Field Trip

Fountain Lake High School Petit Jean Field Trip, May 2, 2014

The Arkansas Geological Survey hosted a field trip to Petit Jean State Park for 26 Fountain Lake High School seniors and science club students. The high school seniors are currently in a college geology course taught by Mrs. Jennifer Cox, a former geologist with the AGS. As far as we could tell, these seniors were ready to show off their geologic knowledge. Two students, whom I understand are brothers, were excited enough to buy Muscadine Grape Juice from the Visitor’s Center prior to the start of our trip. Nothing says geology like a good swig to start your day.

Our first stop was to Seven Hollows Trail. Along the trail, we first looked at liesegang banding and a natural shelter within the Hartshorne Sandstone. Liesegang banding (aka box-work) is created when water percolates through the sandstone and comes in contact with the iron minerals present causing the iron to go into solution. As the rock is exposed to air, oxygen is added to the solution, oxidizing the iron and causing it to precipitate out of solution along exposed joints and/or bedding planes in the rock formation. The iron sometimes precipitates out as box-shaped and triangular patterns. The natural shelter within the sandstone was created as a result of weathering. Again, water percolates through the sandstone and between individual sand grains, causing the grains to loosen and separate from the rock. After millions of years of weathering, large voids are created within the rock. This large void appears to be a prime location for the first of many class photos.HartshorneShelter_ClassPhoto

Senior class photo in a natural shelter within the Hartshorne Sandstone. The natural archway is lined with great liesegang banding features.


Liesegang bands, or carpet rocks based on their square pattern, adjacent to natural shelter.

Our last stop was to Natural Bridge and the turtle rocks above natural bridge. We had some excited young geologists who immediately began to climb on top of the natural bridge.


Natural Bridge (left). Again notice the great liesegang bands in the archway. Young adventurous, soon-to-be geologists climbing above natural bridge to the turtle rocks above (right).


Another senior photo op at natural bridge.

Turtle rocks above natural bridge are some of the best features in Petit Jean State Park. “Turtle Rocks” are unique, mounded polygonal structures that resemble turtle shells. These features are found along the Arkansas River Valley in the Hartshorne Sandstone deposited during the Pennsylvanian Period by ancient river systems. The processes that generate “turtle rocks” are not clearly understood. One explanation suggests that these features were created by a process known as spheroidal weathering, a form of chemical weathering that occurs when water percolates through the rock and between individual sand grains. These grains loosen and separate from the rock, especially along corners and edges where the most surface area is exposed, which widens the rock’s natural fractures and creates a rounded, turtle-like shape. Additionally, iron is leached from the rock and precipitated at the surface creating a weathering rind known as case hardening. These two processes along with the polygonal joint pattern contribute to this weathering phenomenon.




Exploring these great turtle rocks. Everyone was thinking that these features were definitely worth the hike.


After exploring these sedimentary features, we headed back up the trail toward the bus, ready for lunch. I’m not sure how anyone had any energy left after the hike, but it seems most of the students finished their lunch pretty quickly so they could play around on the playground.

After lunch we headed to Rock House Cave, a large rock shelter within the Hartshorne Sandstone. Honeycomb weathering and cross bedding features are easily visible around Rock House Cave. Honeycomb weathering is created very similarly to how the natural shelters are formed (e.g. Rock House Cave, natural shelter along Seven Hollows Trail), in that water percolates through the sandstone, loosening and separating the sand grains from the rock creating a void. Cross beds are diagonal lines that represent movement of large ripples within the sandstone deposited by an ancient river system that existed here 300 million years ago. These cross beds indicate the direction the river once flowed.


Notice the nice cross beds in the middle section of the large boulder above Ms. East’s head.



We ended the day with a final photo session in both Rock House Cave and on the turtle rocks located on the trail.




There are those Sig Figs (FLHS Science Club). They are reminiscing about the day’s awesome geology field trip.

AGS Magnet Cove Field Trip with the Texas A&M Geology and Geophysics Society

AGS Magnet Cove Field Trip with the Texas A&M Geology and Geophysics Society
By Lea Nondorf

On Saturday, January 18, 2014, Bill Prior and I met up with sixteen students, ranging in age from freshman to seniors, from the Texas A&M Geology and Geophysics Society. We started the morning at 9 a.m. with a brief introduction on the geology of Magnet Cove at the Sinclair gas station along Highway 51 in Magnet Cove. Everyone was freezing, but you could tell they were super excited to start the day.

Magnet Cove is an area of unusual petrologic and mineralogic interest that derives its name from the presence of lodestone in the soil and from its basin-like shape. It is located in northern Hot Spring County, Arkansas, about 12 miles east of the city of Hot Springs. The diameter of Magnet Cove is about 3 miles (running northwest to southeast) with an overall area of less than 5 mi2 (Howard, 2007).

The Cove is an intrusive igneous body created by mantle-derived magma that pierced through existing Paleozoic sedimentary rocks (Figure 1, listed as Sm, MDa, and Ms) of the Ouachita Mountains approximately 100 million years ago (Late Cretaceous).


Figure 1. Generalized geologic map of Magnet Cove.

Stop 1

Our first stop was along HWY 270 (Figure 2) looking at the Mississippian Stanley Shale (359-323 million years old). The Stanley Shale is composed primarily of sandstones and shales deposited in a deep ocean basin. These deposits were later faulted, folded, and uplifted during the Ouachita Orogeny (Ouachita Mountains) approximately 323-307 million years ago (early to middle Pennsylvanian Period).



Figure 2. Looking at the Mississippian Stanley Shale. Everyone was clearly excited.

Stop 2

Our second stop was along Ross Cuttoff Road where we looked at the Garnet Pseudoleucite Nepheline Syenite (GPNS). Now say that mouth full five times fast. Although there were just a few boulders in the ditch, the phenocrysts of pseudoleucite were very prominent.


Figure 3. A sample of the Garnet Pseudoleucite Nepheline Syenite.

While learning all about GPNS, one particular nice gentleman stopped by to show us his great garnet, rutile, magnetite, and possibly brookite crystals that he collected from his yard. These crystals were absolutely amazing. As we were looking at his collection, another enthusiastic gentleman pulled up telling us all about his beautiful property and all of the different rocks for us to collect. Well of course we were excited, so we jumped in our vehicles and took off. As we were driving, Bill and I noticed how we were traversing over the syenite rim and out of the basin-Oops. When we arrived at his property, we were amazed by the beautiful view, particularly the view of the Magnet Cove basin. And, he did have a variety of rock, but mostly of red, white, and gray Arkansas Novaculite.



Figure 4. All smiles and thumbs up for Magnet Cove (background).

Stop 3

Here we stopped at the old American Titanium Pit where rutile (chemical composition of TiO2, or titanium oxide) was mined during WWII. We collected pyrite cubes and rutile from this pit. It was pretty muddy, but everyone managed. What troopers!

Stop 4

After lunch, we headed to the old Kimzey Magnetite Pit along Highway 51 where we collected lodestone, rutile, and garnet. A few also found pieces of possible Kidney-Ore hematite and phlogopite. This spot seemed to have it all. Plus, everyone enjoyed using the compass to determine whether or not they had lodestone. A stronger lodestone will really spin the compass needle. Also, the highly magnetic soils in this area make it almost impossible for anyone to use a compass in Magnet Cove.

Stop 5

About a quarter-of-a-mile west of stop 4 along Highway 51, we stopped to collect coarse-grained garnet, biotite ijolite. Ijolite is a feldspar-free, nepheline-rich igneous rock. At this location, we were able to pick up smaller biotite booklets that had weathered out of the boulders present in the ditch.


Figure 5. Checking out the garnet, biotite ijolite. Unfortunately, we needed a pick and sledge to break off pieces of the boulder for collecting, which no one had.

Stop 6

Adjacent to the old Kimzey Calcite Pit about one half mile west from Stop 5, a great carbonatite outcrop is exposed here just west of the bridge. This particular carbonatite looks identical to calcite, but is different in the fact that this carbonatite is an igneous rock derived from the mantle. Carbonatite even fizzes like calcite. Some other minerals that can be found with the carbonatite include carbonate-fluorapatite (light yellow-green), monticellite (brown), biotite, magnetite, pyrite and perovskite. Also, this is the type locality for kimzeyite, a dark brown zirconium-rich garnet (Howard, 2007).



Figure 6. Getting up close and personal with the carbonatite. Check out those rhombs.

Stop 7 and 8

Our last and probably most exciting stop was located IN Cove Creek. Although the day had warmed up quite nicely, the creek was still very frigid (and deep). After Bill showed off his awesome pyrite cubes with molybdenite that he had found in the creek 30 years ago, there was no turning back, we were finding pyrite cubes with molybdenite. Only Bill and I were lucky enough to have waders and boots, but that didn’t stop some of the others from jumping in. We trudged up the creek with no luck and quickly came back to where we started only to find nice pyrite pieces in the creek (of course). A few in the group pulled out nice hand-sized specimens with the molybdenite coating. How awesome!


Figure 7. Leaving the creek with gold in hand, fool’s gold that is.


Figure 8. Success in the cove with nice samples of pyrite.


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Figure 9. Close-ups of the pyrite found in Cove Creek.

Our final stop was just a few hundred feet past the pyrite area. Here we were able to venture to Cove Creek once again to look at jacupirangite, a dark-colored igneous rock composed primarily of pyroxene and magnetite (yes, jacupirangite does slightly attract a magnet). Some brave souls crossed the creek once again to get a closer look at the igneous rock and the lighter-colored syenite dikes. Just FYI, jacupirangite can become very slippery when wet. 😉


Figure 10. Jacupirangite in the creek.


Howard, J.M., 2007. Magnet Cove, A Synopsis of its geology, lithology, and mineralogy. Arkansas Geological Survey. AGES, Brochure Series 004. 11 p.