Cutting a Coal Ball 

Coal balls are aggregates of bedded plant remains that are permineralized in a mineral matrix. They are most common in Pennsylvanian age sediments from North America and Europe, but similar types of preservation occur throughout the geological column. The most common mineral matrix is calcium carbonate, and there are often other minerals such as iron pyrite, magnezium phosphate, etc. To become familiar with preparation techniques, anatomy of fossil plants, and the Pennsylvanian floras of Ohio, we will be cutting, peeling, and identifying the contents of a coal balls from the Upper Pennsylvanian age Duquesne Coal. We will be collecting material at this locality sometime this quarter.

Because you already are familiar with the Coal Ball Peel Technique this exercise will concentrate on the initial cutting and preparation. Coal ball cutting is messy business, so be sure to be dressed in old cloths.

1. Select a coal ball from the bin in Room 02 of Building 7, The Ridges, and make either a full-size or scaled drawing of it. Measure the coal ball and record your measurements as show by the instructor. Label the drawing with your name and the coal ball collecting locality as shown by the instructor.

2. Rinse the coal ball thoroughly to remove dirt, excess coal, etc., and to help avoid having oil permeate the coal ball while it is cutting. You may be able to identify that there are plants in the coal ball even before you begin to cut it. If you see plant materials on the surface, you may want to etch the entire coal ball in 5% HCl for about 1 minute. Allow the coal ball to dry before inspecting it for surface plant material. Remember that the etched surface of a coal ball is quite delicate, so don't rub off the plant materials you are trying to see.

3. Place the coal ball in the vice of the 24" oil-bath slab saw as demonstrated by your instructor. Be sure to line up plant materials such they are being cut in cross sections, and be sure that the coal ball is secure before you begin to cut it.

4. You will want to cut the coal ball into slabs that are about 2 cm thick (3/4"), such that the completely cut coal ball is cut up like a loaf of bread. Crank the vice away from the blade until about 2 cm of the end is in the plane of the blade for the first cut. Close the lid and turn on the saw.

5. Carefully allow the coal ball to approach the blade at an extremely slow speed. Once the coal ball has contacted the blade, you can adjust the rate of cut until is sounds right. The instructor will help you learn the correct sound.

6. After the first cut is completed, turn off the saw and stop the forward motion of the vice. Allow the saw blade to stop completely (or else be prepared to get an oil bath). Open the lid of the saw, and remove the cut slab from the saw. Be careful not to get oil on you, or to let it drip on the floor.

7. Take the slab to the sink and squirt it with liquid dish washing detergent. Rub the degergent over the entire surface of the slab and over any of your skin that is covered with oil.

8. Rinse the slab in warm water to remove the oil/detergent emulsion. Etch the slab as you learned from the "Coal Ball Peel Technique" and set it aside to dry.

9. Now, go back to the saw. Push the vice back until the coal ball is beyond the blade, and crank the vice toward the blade until the next cut will be about 2 cm.

10. Repeat steps 5 & 6 until the vice is too close to the blade to make additional 2 cm cuts. Now, remove the coal ball from the vice. Turn it around with the cut face oriented away from the blade, and insert it back into the vice so that about 2 cm is clamped securely back into the vice.

11. Now repeat steps 4, 5, & 6 until all of the coal ball is cut into slabs, and make peels of all of the faces of the slabs.

12. Now label the slabs and the peels as A-Bottom, B-Top, B-Bottom, C-Top, etc. Use the orange china marker to do this. Mark the shiny side of the acetate.

13. Place the peels in an envelope that is labeled with your name and the collecting locality as shown by the instructor.

14. Try to identify at least 10 different types of fossil plants by scientific name, plant group and plant organ. Circle the plant parts you have identified on the shiny side of the peels, and place a number next to the circle.

15. Make a list of your identifications on the front of the envelope, and indicate the number you have assigned each item on the peels. 


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