This is Mazon Monday post #298.  What’s your favorite Mazon Creek fossil?  Tell us at email:esconi.info@gmail.com.

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With winter arriving this weekend, it’s the perfect time to set out a few containers of Mazon Creek concretions and let nature do the work. Many collectors take advantage of the season’s freeze/thaw cycles to speed up the opening process, by placing buckets or smaller containers of nodules gathered throughout the year outside to weather naturally in the cold of winter.

We’ve done a few posts about the freeze/thaw method. Mazon Monday #77 is “Care and Feeding of Your Mazon Creek Concretions”. The post covers the basic process. There are variations, especially around drying concretions after each cycle.

Freeze Thaw Method of Opening Concretions –Highly Recommended 

Most concretions can be opened by frost action. The water saturated concretion is stressed differentially when it is frozen, creating weakness along the plane of the fossil, wherever in the concretion that may be. It may take many cycles of freeze thaw to succeed in developing a fracture along the plane of the fossil, and some concretions never do succumb. At least 10-15 freeze thaw cycles are recommended before giving up on a concretion. Most concretions that are going to open will open by 40 cycles. The upper limit of cycles is bounded by your patience. Once you reach your limit, go ahead and pound it open with a hammer, knowing that it will probably fracture in many pieces. The alternative is to give it away, or throw it out.

Appendix A of Richardson’s Guide to the Fossil Fauna of Mazon Creek is titled “Freeze-Thawing Technique for Opening Nodules.” Written by Steven D. Sroka and Gordon C. Baird, it provides a clear, step-by-step explanation of the process and even references a few historical accounts of similar methods.

One of the earliest descriptions comes from Captain Lewis Moysey, RAMC (1869–1918), who wrote “On a Method of Splitting Ironstone Nodules by Means of an Artificial Freezing Mixture”, which was published in Geological Magazine in 1908. In 1978, Merrill Foster described his own version of the technique in the original paper describing Essexella asherae (see Mazon Monday #14), “Soft-bodied coelenterates in the Pennsylvanian of Illinois“.

Lewis Moysey was a doctor in Nottingham, Emgland, with a passion for the fossils of the Carboniferous Coal Measures found in the area. His method of processing ironstone concretions included heating, soaking them in water, and then alternating between freezing and thawing until they opened. He first tried heating them until red hot and then plunged them into water. Don’t do that as it resulted in an exploded concretion!

Extract from “On a Method of Splitting Ironstone Nodules by means of an Artificial Freezing Mixture”

Most geologists who have had anything to do with the ironstone nodules in the Coal-measures have been struck by their perverse and refractory behaviour under the hammer. How one nodule will refuse to break under the most well-directed blows, and another, though breaking easily, will exhibit to the disappointed collector a clean bright surface of clay-ironstone, without a trace of that organism that he hoped, and almost had a right to expect, was there. It seems therefore necessary to find some other and perhaps less violent method of breaking them.

…

The method now adopted was to keep the nodules soaking in
water, then to place them in a tin cannister, and surround the tin
with an ice and salt mixture in a pail. After leaving them in the
cold atmosphere thus generated for forty-eight hours, it was found that most of them showed a crack running right round them. On thawing, some were found to be cracked right through, and a light tap with a hammer split them and revealed, in many instances, a very perfect fossil. Others, however, though appearing to he cracked, simply shelled off an outer husk of disintegrated stone, leaving a hard solid core as refractory as ever, which, on again freezing and thawing, sometimes split and sometimes cast off another shell.

From these failures it was thought that perhaps the water did not penetrate into the heart of the nodules in every instance, so several nodules were heated gently to drive off the imprisoned air by expansion, and were then plunged, while hot, into water. After this treatment, in many instances, otherwise refractory nodules were successfully split.

A curious secondary result of these experiments has been the
discovery of a greater proportion of rare fossils in the nodules thus artificially split than in those found naturally broken in the clay-pit. Out of some ninety nodules cracked by freezing, there have been found three specimens of Belinurus, one Palaeoxyris, two specimens of a new shrimp-like animal, and one possibly new animal which may turn out to be a complete but diminutive example akin to the Arthropleura armata of Jordan from Saarbrucken

Moysey wrote a handful of papers about what he found in the concretions, topics included Palaeoxyris, Anthrapalaemon, Vetacapsula, spiders, eurypterids, and other arthropod fossils. British paleontologist Henry Woodward named Eurypterus moyseyi, in his honor.

Unfortunately, Moysey drowned aboard the hospital ship “Glenart Castle” when it was torpedoed in Britol Channel near the end of WW I. A short biography of Moysey can be found here.

On the outbreak of war, he was called to the National Service, and was allotted regimental work in Britain until the final year of the war, when he was detailed for duty in the East. However he was killed before the start of the journey, drowning aboard the hospital ship ‘Glenart Castle’ when it was torpedoed in the Bristol Channel on 26 February 1918. 

Merrill Foster mentions his freeze-thaw method in “Soft-bodied coelenterates in the Pennsylvanian of Illinois“, which was published in Matthew H. Nitecki’s (ed.) “Mazon Creek Fossils” (see page 195). This book contains the proceedings of a symposium on Mazon Creek Fossils held on the campus of the University of Michigan on May 1st, 1978. Foster wrote the following about his method of processing concretions.

The majority of well-preserved specimens were found in concretions that had opened naturally. Very few good undamaged specimens were obtained by splitting open concretions with a hammer. Unfortunately, this is the most commonly used technique by a majority of collectors. Therefore, many specimens collected in this manner are in imperfect condition. I have generally found that if a concretion doesn’t come open with one good solid hammer tap, it probably won’t come open well with any amount of further pounding.

In a Good results in opening concretions have been obtained by a freeze-thaw technique. In this technique, the concretions are first frozen in a container filled with water. Then the ice and the enclosed concretions are melted using hot water. This technique works extremely well on concretions from Astoria. series of experimental studies I made on concretions from this locality, the average concretion took about 20 freeze-thawings to open. The range of freeze-thawings required to open concretions ranged from two to fifty-one. The concretions from Pit ll require a great many more freeze-thawings to open than those from Astoria. I did not make a complete study of Pit 11 concretion opening because of the length of time required, but preliminary experiments suggest that the average opening time might be as much as ten times that required for Astoria openings. I believe the difference in opening time reflects the softer nature of the Astoria concretions. Concretions from both localities have also been opened by leaving them outside to experience the Illinois climate extremes. This method is rather slow, but is apparently effective.

When Sroka and Baird mention “large-volume collectors” below, keep in mind that Baird did a study which included nearly 300,000 concretions from more that 200 shaft mines, and 20+ strip mines (see Mazon Monday #194 and Mazon Monday #281). While processing that hoard of concretions, it’s said the roof of the Field Museum was damaged when it was covered in buckets of concretions during the winter.

The photo below is from a collecting trip in 1981. It shows Steve Ramsdell, Tom Testa, Steve Sroka, and Gordon Baird at CECO in Coal City, IL.

Freeze-Thawing Technique for Opening Nodules
by Steven D. Sroka and Gordon C. Baird

Concretions are collected and processed in a variety of ways depending on the experience, knowledge, and individual preferences of the collector. Field collecting in strip mined areas involves picking up exposed nodules that have weathered out of backpiled Francis Creek Shale overburden. Typically, most concretionary siderite on dump surfaces consists of irregular plates, chips, and tubular masses; this debris is usually unfossiliferous except for trace fossils. Fossil-bearing concretions in contrast display a relatively smooth surface and more regular shape. Nodules on or immediately below dump surfaces are subjected to seasonal frost-wedging and when struck a sharp blow may split naturally along the fossil plane, though others containing mineral-filled fractures may shatter, or resist fracturing almost entirely. In most collecting areas only a low percentage of concretions are found open; the remainder must be split by the collector. In rare sites a majority of concretions are found open; typically such places yield numerous and sometimes spectacular fossils. Because fossils are abundant, autosplitting is natural and common. A reverse corollary applies to places where no concretions are found open; these sites yield barren “nuckers,” and such areas are remembered and avoided by collectors.

Whole concretions must be opened; it is the bane of Mazon Creek paleontologists to hold a tantalizing nodule in hand and still not “have the fossil.” The collector must either risk it all by pounding nodules with hammers on flat rock “anvils” in the mine or choose to wait it out by using a slower method. Too often, adrenalin gets the better of the novice and he pounds away only to get “half the Tully” or a decapitated amphibian. This experience instills wisdom and increased appreciation for patience. The best results in splitting concretions mimic the natural freeze-thawing process, and many good collectors long ago opted for the waiting game, using a freeze-and-thaw approach at home. Historically, freeze-thawing of nodules has been reported by Moysey (1908) and Foster (1979, pp. 195, 201). Moysey (1908), who used nodules collected from a clay pit near Ilkeston (England), first heated them until red hot and then plunged them into water; this process resulted in the nodules’ exploding. Then he tried soaking nodules in water, placing them in a tin canister, and placing the tin in a ice and salt mixture for 48 hours. Upon thawing some had cracked, and a light hammer tap split them. Fi-nally, he gently heated nodules that had not split and, while they were still hot, plunged them into water.

Foster (1979) used the freeze-thawing technique on concretions from Astoria, Illinois, he repeatedly froze and thawed concretions in water-filled containers and recorded the number of cycles required to split them. Foster’s experiments showed that it took an average of 20 freeze-thawings to open his concretions with a range from 2 to 51. Foster also tried this technique with Pit 11 concretions. Although he did not record the number of freezing cycles for the Essex-area material, he suggested (based on preliminary observation) that the average opening time might be as much as 10 times that required for Astoria concretions. He also left concretions from both localities outside in the natural weather cycles to experience climate extremes, concluding that this method is effective but slow.

The common freeze-thawing technique by large-volume collectors is to put the concretions into water-filled plastic containers and leave them outside over the winter. This method is prohibitively slow, taking several seasons to succeed. The method outlined below (successfully used by us since the mid 1970s) can be accomplished all year using a refrigerator or freezer.

1) Whole nodules are placed in water-filled plastic containers for two days, so that the concretions become water saturated.
2) The containers are placed in a freezer for two days to ensure complete freezing.
3) The containers are removed from the freezer and allowed to thaw; then the freezing is repeated.
4) Remove open concretions. During thawing cycles gently tap remaining unopened con-cretions before refreezing.
5) After 12 freeze-thaws, nodules are removed from container and allowed to dry thoroughly.
6) Dry nodules are again tapped lightly with a hammer or tapped together side to side.
7) Nodules that do not split are returned to a clean container with new water and the freeze-thaw cycle is repeated.
8) Experience shows that after approximately 25 freeze-thaw cycles, few added nodules will open; these can be hammered, but remember rock or steel fragments are dangerous! Eyes, in particular, must be protected with shatterproof goggles.

Results using our freeze-thawing method vary from locality to locality. It is found that the majority of localities from the Will County part of Pit 11 had approximately 30 percent of the nodules open after eight freeze-thaws, but certain areas of Pits 11, 13, and 15 in Kankakee County produce results as low as 10 percent yield after 20 cycles. Furthermore, concretions from old spoil piles have already undergone variable exposure to the weather, and average “openability” of nodules is related to other individual properties, such as silt and pyrite con-tent. Concretions cored by pyrite resist freeze splitting and, in many instances, even the hammer.

References

Foster, M. W. 1979. Soft-bodied coelenterates in the Pennsylvanian of Illinois, pp. 191-267. In M. H. Nitecki (ed.), Mazon Creek Fossils. Academic Press, New York.

Moysey, L. 1908. On a method of splitting ironstone nodules by means of an artificial freezing mixture. Geological Magazine, 5(5) / 220 – 222