FX3- Limestone & Iron Oxide
This experiment is the first attempt to make a fish fossil within a limestone matrix. I used a ground Dolomite limestone powder of the type used in gardening. I then added some very fine iron powder to see if it would oxidize and provide the fossil with the dark red oxide coloration found in the fossils from the Green River formation. The fish I used were thicker and a bit larger than used in other experiments which would explain the oil that was found. When the sample was first removed from the reaction vessel it was smooth and glossy black but soon developed numerous fractures. It appears that the residual hoop strain from the stainless steel cylinder crushed the sample when the hydraulic pressure was released. Maximum pressure on this sample was 2500psi whereas the pressure on FX2 was only 1500psi which resulted in no fractures at all. Note the color differences from using multiple light sources and not adjusting the camera white balance each time.
One thing that I did not expect to find was a small amount of oil released both in the steam that was vented into a pan and in the headspace above the piston. The oil was very thick and dark like used motor oil. It also appears that some of the oil remained in the limestone. The brown crumbly looking material in the first picture below was very light and airy as if a foam had dried. It was very crispy and collapsed when handled leaving a brown oily residue on your fingers. After sitting in the open air for a few days, I discovered that it had absorbed moisture from the air and melted into a sticky brown residue. It was later evident that the limestone itself also absorbed moisture and softened as well.
FX3 Fossil Experiment Details:
1. Used 4 inch inner diameter tie rod reaction vessel. Air only within the vessel.
2. Used Aflas piston and piston rod O-ring seals with PTFE cylinder seals on the end plates. All seals remained intact throughout experiment. Zero leakage.
3. Used Dolomite limestone, Espoma Organic Garden Lime: 1.42KG; Water: 280 gm; Fine iron powder, 320 mesh: 200gm.
4. Blended in a household style blender into a smooth, thick slurry. Poured out onto an absorbent mat to thicken.
5. Assembled the reaction vessel per standard procedure.
6. Added approx. 1 inch of slurry to bottom of cylinder, added three fish, another 1 inch of slurry, two more fish and then a third layer of slurry.
7. Completed assembly of the reaction vessel and placed in oven.
8. Slowly, over a period of 5 hours, applied hydraulic force to rod end starting at 3000 lbs or 225psi to sample and ending at 33,300 lbf or 2500 psi to sample. Pressing out the water from limestone slurry and fish resulted in approximately 22% reduction in volume.
9. Raised oven temperature to 480F. 23:20hr 11Aug2022
10. Monitored inlet and outlet pressured to maintain 700 -1000 psi steam pressure.
11. Steam pressure got up to 1200psi 20:00hr 12Aug2022. Slowly vented reaction vessel to allow sample to dry out. Oven Temperature remained at 480F.
12. Turned oven off to cool at 07:00hr 13Aug2022. Reaction vessel had 100 psi remaining steam pressure. Captured all liquid that came out of vents. Plan to run all gasses through a condenser coil to minimize vapors and odors on future tests.
13. Removed sample from chamber 22:30 hr 13Aug2022.
Conclusions and Observations:
1. Compression time, 5hrs. Heating time at 480F, 32.5 hrs. Cooling time, 14.5 hrs. Total processing time, 52hrs.
2. The sample was coal black with a mirror like finish on the sides of the cylindrical sample.
3. Residual hoop stress in the stainless cylinder fractured the sample as hydraulic force was removed. Need to find a way to triaxially decompress the sample if using this high of compression force or run at lower forces. Earlier run, FX2, at 1500psi compression, did not fracture.
4. After the liquid that came out of the chamber cooled, a layer of thick black oil remained. approximately SAE90 in viscosity and very slippery like gear lube. After a few weeks at room temperature the oil dried further and became tacky.
5. A small piece of “Limestone” was submersed in water and crumbled back into a clay like consistency when crushed between fingers.
6. Fish fossils were black in color.
7. The iron powder was added to see if any of it would oxidize and turn the matrix or the fish remains reddish brown or crystalize in some way to bind the matrix together into stone. The iron powder turned black and did not oxidize red in color. Since the “stone” disintegrated when submersed in water, it did not contribute to binding the limestone together either.
8. Need to better understand how iron oxidation process occurs and where does the oxygen come from in those fossils found in the ground?
9. In the space between the cylinder and piston rod there was a very crispy, black/dark brown foam like material that left a greasy residue on my fingers when crushed. After sitting in the air for a day or two it must have absorbed moisture and melted into a dark brown residue.
10. It was observed that the limestone and the fossil also contained the black oily substance which is not normally found in the natural fossils. It is theorized that in natural fossils, the water pressure from below the fossil bearing strata strips the fossil layer of the biological liquids as the water moves up and through it. If this is true, then it also means that the minerals that bind the matrix together and per-mineralize the fossils may come from below the fossil layer as well.
11. I need to better understand how the dissolution and re-crystallization of minerals occur in nature such that crystal growth can occur within a void or fossil or act as a binding agent for the formation of sedimentary rock.
12. After a few weeks, it seems that the limestone had also absorbed moisture from the air and become softer. When scratched with a needle the particles come apart easily but tended to stick to each other. This makes sense given the fact that the crispy brown foam absorbed moisture and melted into a gooey brown liquid.
13. Quite possibly the oil from the fish interfered with cementation of the limestone and oxidation of the iron powder. Hopefully an inorganic chemist or geologist will be able to help us understand what is happening.
