Sectioned and Polished Fossils

[Thomas.Dodson]

I've never put much time into sectioned and polished fossils, usually just because I don't usually collect material that would look well cut over whole. While preparing a trilobite I collected in Illinois over the Summer and I was cutting sections off the matrix bottom so the matrix lay flat as a stand. To my surprise I ended up cutting thin sections through a Favosites coral that piqued my interest. Coincidentally, this was at the same time @FranzBernhard posted his thread demonstrating a low-cost approach to polishing and sectioning small carbonate rocks and fossils by hand.

With such a handy guide put forward at a perfect time I decided to try my hand at sectioning and polishing fossils. I was waiting on grit polish in the mail for a while and that has now arrived which allowed me to finally try some sections myself. I figured I'd post the humble results here so as to encourage more people who might be interested in trying this.

 

I've cut lots of rocks before but this was my first time attempting polishes. The uneven cuts from some of the specimens are noticeable in the polish. I tried to grind some of the surfaces even before polishing but this was more difficult for the hard material. Oh well. I think I can improve the fine polish on a lot of these by putting more time into them but I think this was good as a first attempt.

 

 

[Thomas.Dodson]

And the thin Favosites cuts that inspired the attempt.

 

 

 

[Thecosmilia Trichitoma]

Nice. How long does it take for you to complete cutting and polishing one of those?

[Thomas.Dodson]

10 minutes ago, Thecosmilia Trichitoma said:

Nice. How long does it take for you to complete cutting and polishing one of those?

Cutting went quick, a minute or 2 for most of them. Polishing took longer, around 15-20 minutes each maybe. Some of the softer ones took less.

[FranzBernhard]

Very nice, @Thomas.Dodson, thanks for sharing.

Polish looks really good, the only thing is to spend a little bit more time in coarse grinding - removing that saw marks.

 

12 hours ago, Thomas.Dodson said:

Polishing took longer, around 15-20 minutes each maybe

It depends also very much on the size. I need the same time for intermediate sized and easy to polish specimen, say of about 30cm² size, though. Very small specimens, say around 10 cm², need only about 5 minutes. Notice: Everything done by hand, no rotating polishing discs etc. 

 

But don´t forget the time for coarse and fine grinding. Fine grinding is also a matter of minutes, but coarse grinding time (done by hand!) really depends on the flatness of the saw cut. Maximum time spend here for a specimen was 2 (two!!) hours, coarse grinding with 400 grid removing the saw marks*. But the cut was also really, really bad.

 

*Note: I have gone back to the stainless steel pot for coarse grinding. It gives a much better grip / abrasion than the glass plate or the tile. When saw marks are removed, I am going to the glass plate and again 400 grid for a short time. This gives already a much finer surface than the bottom of the steel pot.

 

Franz Bernhard

[Bob Saunders]

I have seen some really nice polishing of cut stones  using the diamond pads for granite counter tops on a 4 inch right angle grinder. probably clamped right side up not hand held. Some pad sets now under $45.  

[Thomas.Dodson]

Polished Sections Round 2. Among the Fox Hills concretion pieces I have everywhere I remembered I had some pieces from Whiskey Bridge in Texas I kept around as an example of the matrix. I figured these would be perfect for sectioning and went to work.

 

Learning from my experience the first time, I started these new slabs with more coarse silicon carbide (220) to make sure I got rid of those pesky saw marks. Starting with the more coarse grit also seemed to help the polish at the end by creating an even flatter surface. I used a glass plate for every step of these (220 grit, 600 grit, 1200 grit) except for the final step which I used Cerium Oxide on a jean leg section. I had Cerium Oxide around so I used it although some polishes might be cheaper. I think these turned out really well.

 

[Thomas.Dodson]

I like the individual coarse grains of matrix in this one.

A sample from a different Stone City outcrop in Texas.

Some of the additional Fox Hills slices. The polish on the bivalve sections is amazing. The dark sections are pieces of wood that are common in the concretions from this site.

 

This makes for a great thing to do if you live in a cold climate like myself and can't go fossil hunting again until the snow melts. I didn't have anything I still needed to prep so this works great. Besides this the only fossil related thing I had to do was plan excursions for the spring.

 

 

[fifbrindacier]

I love the set of colors.

[FranzBernhard]

Sweet!!  Thanks for sharing your experience and specimens!

 

3 hours ago, Thomas.Dodson said:

I didn't have anything I still needed to prep so this works great.

Huh!?! How can this happen?? 

 

I would like to share the two-hour piece mentioned above - it contains also many quartz-rich clasts, one reason for the lengthy grinding time.

Franz Bernhard

[Ludwigia]

Nice job on those Whisky Bridge pieces! Keep up the good work. It's a fascinating occupation.

I've been cutting, grinding and polishing for years using a multi-purpose machine with a diamond saw for cutting and a rotating steel plate for grinding and polishing. This goes back to the days when I was collecting agates and similar minerals in need of this type of treatment. When I started collecting fossils I did all of my prep by hand, and there were always some where the matrix was just too hard to work, so I started cutting them and also soon came to realize that the results were not only sometimes aesthetically pleasing, but also could be quite instructive about the inner structures of the fossils.

Here is a link to one of the albums in my gallery dedicated to the subject.