Magnet Cove, Arkansas
Current Status: most sites closed.
Magnet Cove! Wow, how to write a short article article about the most mineralized 5 square miles in Arkansas? Well, we're off on a try at this task!
As times change, collecting areas come and go. Many of the collecting areas from our college days are shut down. Some were closed due to federal regulations, others were closed for insurance reasons. Here is some history about the region.
History of Collecting
Before 1820, locals recognized there was something different about this area. Their compasses went haywire as they walked across the ground. Then by the 1840's people began to notice a variety of unusual minerals. Later in the 1850's many specimens had been shipped to Europe and examined by German mineralogists and Magnet Cove's fame as a collecting area began.
Hot Spring County
Magnet Cove Historical Marker
"This is Magnet Cove which covers an area of irregularly oval shape about five square miles. The cove is made up of volcanic rocks which have gradually been forced to the surface of the earth. It was probably not an eruptive volcano. About 42 distinct mineral species have been found in the cove and many of the mineral types and combinations are of world-wide interest to mineralogists because they are known to occur in only two other localities, the Ural Mountains and the Tyrolean Alps. Here was the home of James Sevier Conway from 1834 until after 1840. Here the eminent English geologist G.W. Featherstonhaugh visited in the autumn of 1834."
Truly a world-famous site
Magnet Cove has provided many heydays for rockhounds, collectors, mineralogists, and geologists. And it continues to do so when access to sites is available. There are 2 comprehensive publications on Magnet Cove. The earliest is a part of the Arkansas Geological Survey's Annual Report for 1890 - "The igneous rocks of Arkansas" by J. Francis Williams and the most recent is USGS Professional Paper 425 (1963) by Erickson and Blade. Both of these reports are long out-of-print, but may be reviewed at major university libraries. William's report goes into some detail concerning the minerals and their occurrence at Magnet Cove and the USGS report details the chemistry, along with some additional mineralogy, of the igneous rocks. Many of the sites named are the same, despite the decades of time separating these two publications. There have also been a series of articles in recent years in Rocks and Minerals magazine on various minerals and sites of this area.
Whenever there have been mining ventures, there have been collectors following close behind. This is especially true at Magnet Cove. Some serious mineral collecting of the area took place before the 20th century, but most collecting has gone on during the 1930's through the 1990's. Mining of rutile, though short lived in the early 1940's, provided an area that was accessible for 40 years to collectors.
Investigations into molybdenite along Cove Creek resulted in the discovery of a deposit of pyrite that has been an available site since the early 1950's. The quarrying of carbonatite, an igneous carbonate rock, in the mid-1950's opened up a collecting area that was available for 25 years. A new mineral to science, a zirconium-rich garnet named kimzeyite, was described from this site, which continues to be the only location where good crystals of kimzeyite are collected. Even road and bridge improvements, and gas line cuts, provided some well received collecting sites until the lush vegetation took them back over.
A railroad ballast quarry, the Diamond Jo, saw few collectors until the late 1970's. The significant discovery of tiny vugs and pockets containing a host of microminerals had to wait until several things happened. It was amazing what a couple of dedicated mineralogists and some field collectors and geologists, who were willing to share anything they recovered, accomplished. And kind words must be mentioned of the owner, Henry deLinde, who due to his enthusiasm for minerals and his fellow collectors, allowed the many visits necessary to accomplish this task. Due to their efforts, two new minerals to science, delindeite and lourenswalsite, were described as well as several new species for Arkansas.
It seems that at Magnet Cove, as one site plays out or is closed off, another always opens. After the Diamond Jo discoveries, Union Carbide began mining operations in the mid- to late 1980's at their Christy deposit, a previously well known surface collecting site for brookite and smoky quartz. Mining revealed not only these minerals, but a host of others including perhaps the best kolbeckite crystals ever discovered anywhere in the world, taeniolite (a lithium mica) and lenoblite, a very rare, poorly described, vanadium mineral. Now that the Christy has been reclaimed, another quarry just southeast of the Magnet Cove intrusion is actively operating in the baked contact zone. Interesting minerals occur in thin veins here, the result of passage of fluids and vapors released by the cooling magma, penetrating outward into the surrounding country rock.
So the collecting goes on. Some individuals are always able to find a few minerals in this area. The area built its reputation early with collectors for the abundance of titanium-rich minerals, like rutile, brookite, anatase, and perovskite. Now, as the years have passed, Magnet Cove has yielded species both new to science and to Arkansas.
Magnet Cove is a 100-million-year old igneous intrusion (mass of igneous rock) of some rare and unusual rock types - all derived from a melt that was originally a CO2-rich basaltic liquid in the earth's upper mantle. The intrusion's piercing style resulted in a steep, near vertical contact with the country host rock, Paleozoic shales and novaculite. It is likely that the intrusion never reached the surface. Only one geologist in the 1930's described anything like a vent. It is probable that what he described, though volcaniclastic in appearance, was a steep-walled breccia pipe or explosion zone as has been noted in the smaller pipe at Potash Sulphur Springs, some 4 miles west of Magnet Cove.
Magnet Cove was a large piercing body, some of which had already become a crystalline mush by the time it reached the elevations of its present exposure. It did not reach the surface, but caldera collapse resulted in injections of molten material into circular fracture zones. Caldera collapse happened several times. The resultant outcrop maps at the present level of erosion take on a somewhat circular pattern for some of the major units. Erickson and Blade called the intrusion a ring-dike.
The silica-deficient molten liquids (no free quartz will form from these melts) underwent several stages of crystallization between injections and caldera collapse. Thus we have a series of igneous rocks with unusual compositions, all ultimately related to the mantle parent.
Significant contamination from the crust appears unlikely since a piercing injection style is less likely to incorporate and assimilate much host rock. The intrusion sequence (that is, the order of emplacement of the igneous rocks) began with a fine-grained syenite equivalent called phonolite/trachyte, then a core of a very silica-deficient rock - ijolite - was emplaced. Then came a variety of nepheline syenites around the oval rim and afterwards some marginal satellite bodies composed of pyroxene and magnetite (the rock jacupirangite) between the outer ring and the country rock. Finally, in the central core, calcite-rich bodies of carbonatite were emplaced. I know the average reader will not understand the names of these rock types (even many geologists will have to run and dig out their old rock classification charts, not to mention our computer's spell checker going ballistic!), but I have only briefly touched on the geology of this complex intrusion.
Magnet Cove mineral collectors come in two types: those who are micromounters and those who love black or dark colored minerals. You might laugh at this, but both have their place at Magnet Cove!
Micromounters discover unique crystals of many types and are not limited to a well known location to hunt for specimens. Any old rock will do, just so long as when it is broken, it contains cavities. That's where you hunt for new minerals with a microscope.
Those rockhounds and collectors who like black minerals, sometimes perched on black minerals, will continue to hunt for brookite crystals on smoky quartz, loose clusters of magnetite, perovskite, spinel, and hercynite in the soils overlying the carbonatite zones, single and small clusters of schorlomite garnet in the soils formed from the central core of ijolite, and rutile black from the presence of niobium and iron in the mineral's structure. Small dark brown kimzeyite garnets, along with shiny perovskite, contrast nicely with white calcite, yellowish carbonate-fluorapatite, emerald green biotite, and brown monticellite.
Certainly there are some interesting white and other colored minerals from the area also, including fine-grained nepheline and potassium feldspar pseudomorphs after leucite, albite bowties after an unknown mineral (almost looks like it's after stilbite!), albite "rice grain" rose specimens, iron pyrite coated with molybdenite so it looks a little like galena to the unexperienced eye, masses of naturally magnetic magnetite (lodestone) and many others too numerous to name.
Too many collectors, with too little manners...
Since most of the older well known locations are presently closed to collectors, I thought about not even mentioning specific sites, but I knew this would cause an uproar amongst our visitors so I will mention a couple of locations that can usually be accessed without causing a problem with landowners. You must realize that literally *hundreds* of geologists and *thousands* of collectors have visited this area in the past 50 years. Many of the landowners are fed up with even being asked for permission. So don't press your luck. When a landowner at Magnet Cove says they will call the Sheriff, they probably already have!
The Mo-Ti and the pyrite dig are adjacent to each other a couple of miles upstream on Cove Creek from the AR Hwy 51 bridge. Digging in the creek and along the high bank on the south side of the creek has been a popular pastime for many a rockhound. Aside from just pyrite, one can find small black smoky quartz crystals, brilliant lustered brookite crystals, orthoclase feldspar, greasy gray films of molybdenite, and even an occasional specimen of iridescent pyrite.
AR Highway 51 bridge and roadcut - typical outcrops of coarsely crystalline carbonatite along the road are almost devoid of any other mineralization, but specimens of carbonatite from the gravel bar on the south side of the bridge often contain interesting minerals. Look for those specimens with lots of dark spots or grains. Take them back and soak in vinegar or acetic acid to reveal some interesting minerals.
These are the only two public sites where rockhounds can go without potentially having a serious problem with landowners. ***Do be nice wherever you visit in this area and be certain to pickup your trash!*** Several sites have been closed in this area due to this single problem.
Aside from the two mentioned reports on Magnet Cove, here are several other available literature sources for information on Magnet Cove:
Collecting Arkansas Minerals - A reference and a Guide, by Art Smith, Jr.(1996). This book is apparently either out-of-print or unavailable at this time.
Mineral Species of Arkansas, a digest by J. M. Howard (1987) Arkansas Geological Commission Bulletin 23. To order this and other available publications and free pamphlets from the AGS, contact their website at http://www.geology.arkansas.gov/home/index.htm
The Arkansas Issue of Rocks and Minerals, 1989, July-August issue has several articles of interest concerning collecting minerals from Arkansas, including Magnet Cove.
If you happen to have the American Mineralogist series available at a university library, check the subject indices for Magnet Cove to find some articles.
Howard, J. M., 1999, Brookite, Rutile Paramorphs after Brookite, and Rutile Twins from Magnet Cove, Arkansas: Rocks & Minerals, v. 74, no. 2, p. 92-102.
Magnet Cove minerals are famous for being black, or having black on black minerals. Difficult to photograph? Yes they are! Here's some photos, as best as we can do.
Rice-ball rosettes of albite. Several hundred pounds of specimens from thumbnails to large cabinet size were recovered from a cavity on the south side of Cove Creek.
The fellow who discovered the cavity accidently fell into the hole while walking down the creek bank. After his broken leg healed, he returned with a helper and excavated the pocket. It began at creek level and extended 18 feet below the normal stream water level. This piece is about 5 inches in height.
Clusters of magnetite crystals are sometimes recovered loose in the soils of the central core of the intrusion. Most attractive specimens come from the weathering of calcite-rich carbonatite. Individual magnetite crystals are 1 inch across.
Brookite on smoky quartz has been collected in the Magnet Cove area since before 1850. Attractive large crystals are scarce, whereas smaller crystals are abundant in the soils at several locations. Silica for the formation of smoky quartz came directly from the host rock, the Arkansas Novaculite. These brookite crystals measure 1/2 inch across and 3/8ths inch thick.
Weathered biotite (mica) showing growth zones in a relatively well formed crystal. The mineral is probably now converted to vermiculite. Flakes and small books are relatively abundant in the residual soils of the core area. Because mica splits easily into thin sheets, it is called a "book" when the crystals have some thickness. Some books of vermiculite over 6 inches across and 2 inches in thickness were recovered in the early 1960's. The specimen is 1 inch tall and 1/4 inch thick.
Rutile paramorph after brookite. A paramorph is a mineral of the same chemical composition, but which crystalizes in a different crystal system as the original it replaced. In this specimen, brookite formed first and as the temperature rose, rutile began to replace it. Both minerals have the same chemical formula, but are stable at different temperatures. So this example retains the external crystal shape (form) of brookite, but is now composed of numerous interlocking small crystals of rutile. This crystal fits into a 1 1/4 inch perky box.
Small rutile eightling mounted in a 1-1/4 inch perky box. Rutile eightling twins are perhaps the most famous mineral form known from Magnet Cove. Many were discovered by early collectors, but presently only a few collectors have been able to gain access to where they occur loose in the soils. Note thumbnail for size comparison.