FX5-Limestone & 33% Pyrite
This is our second attempt to make pyrite in a limestone matrix. We also placed 6 small fish and the end of a wild turkey feather between the layers. We learned in FX4 that there are several types of Iron sulfide which I initially thought was just Pyrite. However Pyrite is actually Iron DiSulfide, FeS2 and has 46.7% Iron and 53.3% Sulfur by weight. Plain iron sulfide, FeS, is black in color and is 63.5% Iron and 36.5% Sulfur by weight. So for FX5 I used the formula for FeS2 and made the Pyrite portion 33% of the total mix. Another thing I didn’t previously know about pyrite, is that it is a very exothermic reaction as it forms. As I was compressing the sample the temperature shot up to over 180F but by the time I noticed it, the temperature was dropping rapidly so I assume it had been at the boiling point. If that is true then all the water boiled out and the reaction stopped. It would have been interesting, had there been enough water pressure to prevent boiling, to see just how high the temperature would have gone. Previous to this experiment, I had always thought that the heat required for this type of fossil to form came from geothermal or volcanic energy. But now it seems that a tremendous amount of heat can be generated by chemical reactions as sulfur and other chemicals move through the ground water. Even if the reactions were very very slow in nature, it would essentially have been an adiabatic process that deep in the earth and the temperature could have slowly risen for quite some time. The leftover limestone mix was placed in a zip lock bag and left on the table. Within a few hours the mix suddenly got very hot, melted the plastic bag, and started steaming. The last picture is of the limestone mix after it had reacted and partially oxidized in the open atmosphere.
While assembling the fixture for this experiment, there were two fish left over in a shallow pan. Within about 3 weeks they were beginning to decompose. It dawned on me that this would be a great time to begin a study to see if one could distinguish a freshly buried fish from a slowly buried fish that had died in shallow water. Back in FX2 there were two different types of fish that were beginning to decompose and they ruptured under the pressure. You will notice in the photos below that the skin is already beginning to sluff off and the fine tissue at the ends of the fins are almost gone. Is this consistent with what may have occurred when natural fossils were forming? I don’t know, but I believe that it is very close to what is actually observed in streams and lakes today. It will be very interesting to see how they turn out in FX6.
FX5 Fossil Experiment, Limestone and Pyrite
1. 22Sep2022
2. Prepare reaction vessel according to standard assembly procedure.
3. Limestone used is powdered “naturally reprecipitated calcium powder”, 93%CaCO3, Iron Fe 0.27%, Calcium (Ca) 37%, sold by “The Seed Supply”.
4. Iron powder, very fine 320 mesh (~0.0017in max. dia.), ArtMolds p/n SM400241R
5. Powdered Sulfur, 99% pure, CAS # 7704-34-9
6. Limestone Powder 1.00KG, Fe powder 232.8gm, Sulfur powder 267.3 gm (Pyrite 33.3% by wgt)
7. Combined sulfur and iron powder dry then added limestone and mixed dry until smooth consistent color.
8. Added water to achieve a smooth clay like consistency.
9. Added ~1inch layer 1, End of wild turkey feather, ~1 inch layer 2, 6 small fish, ~1 inch layer 3 per standard assembly procedure.
10. Placed vessel in oven and placed thermocouple #1 against cylinder using stainless hose clamp. T/C#2 was left hanging to measure oven air temperature.
11. 22Sep2022 21:35, Attached inlet outlet and vent lines to vessel and set hydraulic ram force, Fhyd, to 5,000lbf or 375 psi on piston. Dim “A” is measured from the hydraulic ram coupling and the bushing just to the right of the coupling using a digital caliper. A initial = 2.972”
12. 22:35 Tcyl=168.9F Tair=76.9F, an exothermic reaction is occurring but the temperature at this point was dropping rapidly so I believe that the temperature hit the boiling point and pushed all the liquid water out of the sample, ending the reaction. This was later confirmed by a porous looking structure and lack of crystals as found in the FX#4 experiment. Future experiments will have the water pressure increased to 900psi as soon reaction vessel is connected and before initial compression begins. This also confirms the need for a digital chart recorder to see a trend of what occurred.
13. A second possibility might be that the exotherm was short lived, but it seems that the temperature drop would have been much slower afterwards.
14. 22:45, Tcyl=133F
15. 23:38, Tcyl=101F, Increased Fhyd=10,000lbf (750psi compression)
16. Note: At 23:00hr the leftover matrix was sitting on the bench at room temp. and was light gray in color. When we returned at 23:38 to raise the pressure, the leftover matrix had tuned black and was too hot to touch. It had also melted the plastic bag and was steaming. A= 2.898”
17. 23Sep2022, 00:15 hr, A=2.898” so I believe that the exotherm caused the sample to harden so I increased Fhyd=15,000lbf to start it moving again then left it at 13,000lbf.
18. 00:20hr, A=2.877”, 00:50hr A=2.876”
19. 01:00hr increased Fhyd to 20,000lbf. Increased water pressure to 900psi, Opened inlet valve, inlet pressure went to 900psi, closed valve.
20. Shut off pump and rotary converter, Fhyd holding at 20,140lbf, A=2.851”
21. 01:15hr, A=2.843” Turned oven to 250F
22. 03:24hr A=2.763”, Tcyl=257F, Pin=900psi, Pout=0
23. 03:25hr set oven to 350F
24. 09:40hr Tcyl=360, Pin=880psi, Fhyd=17,340lbf, Pout=180psi, A=2.670”
25. 09:50hr Turned hyd pump back on and Fhyd came back to 20,000lbf. Raised oven temp to 500F.
26. 12:02hr Tcyl=476F, Fhyd=18,385lbf, Pin=930psi, Pout=600psi, A=2.601”
27. 15:00hr, A=2.564”, Tcyl=503.2F, Tair=501.7F, Pin=960psi (reduced to 900), Pout=870psi
28. 20:55hr, Found Fhyd at zero, not sure if power glitch may have caused relay to drop out or if it just leaked down. Pumped back up to 20,000lbf. Tcyl=501F, Pin=920psi, Pout=860psi, A=2.529”
29. 25Sep2022, A=2.509” press and temp unchanged.
30. 26Sep2022, A=2.503” Tcyl=503F, Press unchanged.
31. 27Sep2022, A=2.494”, Tcyl=500F, Press unchanged, Reduced oven temp to 400F.
32. 28Sep2022, 09:45hr, Tcyl=413F, Pin=400psi, Pout=320psi.
33. 18:05hr, Tcyl=413F Pin=380psi, Pout=320psi, Reduced oven temp to 300F.
34. 19:46hr, reduced Fhyd to 10,000lbf. Tcyl=320F, Tair=306F, Pin=170psi, Pout=100psi, the lower outlet pressure and a sulfur smell indicates the seal on outlet end of cylinder has started leaking.
35. 20:00hr, began venting steam through condenser coils.
36. 29Sep2022, 09:20hr, shut off oven and opened doors. Set Fhyd to 0lbf. Let cool.
37. Removed sample, final actual sample thickness is 2.103”, total compression of sample was 0.47” which means the initial sample thickness was 2.573”. Total reduction during test was 18% by volume.
Results and Observations
1. Slowly compressed for 4hrs. Heated for 152hrs. Total process time 156hr.
2. The sample was cracked open with a sharp knife and hammer, going slowly around the circumference of the sample approximately 3/4 inch from each end, exposing the fossils.
3. The limestone was very hard as in FX4 however it contains bubbles or appears porous which makes sense due to the high temperature exotherm which occurred at the beginning of the experiment.
4. Under a microscope there were no crystals of Pyrite on the fish remains as seen in FX#4.
5. Within a few of the bubbles or pores, there appeared to be clear crystals beginning to grow but was not able to determine what minerals these were made of.
6. One piece was viewed under a microscope and found to contain small golden particles that appear to be Pyrite. These particles appear to be the iron powder that was transformed into Pyrite directly or at least on the surface of the particles.
7. The exothermic reaction obviously generated a lot of energy. I am not sure how much of the reaction occurred between the iron and the sulfur or perhaps the sulfur and the limestone as well. Up to this point I have always assumed that the heat of fossilization came from geothermal or volcanic sources, however this experiment has proven that a great amount of heat can be generated from the reaction of the layers as they are being laid down and chemicals and minerals being carried by the migration of water up through the layers as the previous layers are compressed by subsequent sedimentation and settling.
8. Need to better understand the chemistry or cementation rate/ conditions under which the Limestone powder binds together into a waterproof or weather resistant rock.
9. It appears that 500F may be too hot for the O-rings. Will limit the temperature to 480F in future tests as in FX#4. Will also raise bolt torque to 15 ft-lbs.
10. There were 2 fish that would not fit into the fixture. They died a few days later. The last three pictures above are the fish after approximately 4 weeks floating in still calm water. They will be included in FX#6 to observe the difference between being fossilized fresh and after x weeks of decomposition.
