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Author Topic: Cutting Ammonites  (Read 1764 times)

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Enchantra

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Cutting Ammonites
« on: March 23, 2019, 01:08:31 PM »

If I manage to get a hold of some small whole pyritized Ammonites, anyone of my friends willing to cut them in half so I have matching pairs? Some may be small ammonites - 10 -15mm. Please let me know if you are up to the task. Thanks.

vitzitziltecpatl

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Re: Cutting Ammonites
« Reply #1 on: March 23, 2019, 07:54:12 PM »

Are these the ones from back east somewhere? I saw really cool specimens online once upon a time. If so, is there time to order any extras?

BTW - I'm pretty good with a saw. :-)

rocks2dust

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Re: Cutting Ammonites
« Reply #2 on: March 24, 2019, 10:32:18 AM »

I've seen them from Ohio and England. The ones I had (or have somewhere) were around 1/2 x 1/16 inch and too crumbly to saw. Beautifully detailed little things, though easy to break. Maybe larger/thicker ones could take being sliced, but pyrite can become unstable (and no form of stabilizing will hold it together). I've seen larger Russian pyritized ammonites sold that were sliced, so it can be done.
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vitzitziltecpatl

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Re: Cutting Ammonites
« Reply #3 on: March 24, 2019, 01:24:40 PM »

Yeah, I wondered about pyrite. Even on a 4" saw.

I think the fossils I saw were from New York, and a quick search just now even talked about keeping them in a humidity controlled environment. Evidently that type of fossil is inherently unstable over longer time periods.

Enchantra

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Re: Cutting Ammonites
« Reply #4 on: March 24, 2019, 03:08:23 PM »

The ones in question are from Eastern Europe/Russia.
https://www.ebay.com/itm/2x-AMMONITE-15mm-Pyrite-Mineral-Fossil-fossilien-Ammoniten-France-Dino/323736915838?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2648

I have four I have won so far on Ebay.  Have another two over the week that I have bid on that I could end up with as well.  All from the same seller.

Enchantra

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Re: Cutting Ammonites
« Reply #5 on: March 24, 2019, 03:10:04 PM »

The ones in question are from Eastern Europe/Russia.
https://www.ebay.com/itm/2x-AMMONITE-15mm-Pyrite-Mineral-Fossil-fossilien-Ammoniten-France-Dino/323736915838?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2648

I have four I have won so far on Ebay.  Have another two over the week that I have bid on that I could end up with as well.  All from the same seller.

Actually that set is from France, the seller is in the Czech Republic.
However other Ammonites from them I have won are of Russian origin.

gemfeller

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Re: Cutting Ammonites
« Reply #6 on: March 24, 2019, 08:29:46 PM »

I have several polished ammonite halves from France and Germany that have some sort of metallic content: not sure whether it's pyrite, marcasite hematite or???  Some have been in my display tray for 25 years or so and I've not seen any deterioration.  I also have some wonderful pyrite casts of whole ammonites from Germany I purchased many years ago.  They don't show any deterioration either. 

Images of both tomorrow when I have some daylight.
 
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irockhound

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Re: Cutting Ammonites
« Reply #7 on: March 24, 2019, 08:41:44 PM »

Not being a mineralogist  I am only commenting on my material.  I have many different Pyrites and Marcasites.  The Marcasites much more readily decay than the Pyrites and of the Pyrites I have many in the same storage conditions and some have never shown any deterioration and some have literally turned to dust.  I am sure there can be varying amounts of iron in the Pyrite that could fend off the decay process and Pyrites with lower amounts going quickly and higher amounts not having a problem.  Some of the Pyritized shells that I have came from the quarry almost gray.  I have a large Italian Cube over 4" square that is problem free.
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vitzitziltecpatl

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Re: Cutting Ammonites
« Reply #8 on: March 25, 2019, 08:01:29 AM »

Yeah, I have no experience with mineral collecting so I just referred to what people who collected the ones in New York had written about specimens from that location. I have some old pyrite decorative dust-collectors. They're solid.

As for slicing them, Robin showed me listings for some online that look pretty thin. I can split most anything on a small saw, but if it won't hold together you'd get glittery fish tank gravel.

rocks2dust

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Re: Cutting Ammonites
« Reply #9 on: March 25, 2019, 09:08:23 AM »

Those of us who live in dry climates have a better chance of warding off the problem of rot. Moisture + oxygen seems to trigger the unstoppable reaction called "pyrite disease" or "pyrite rot" in pyrite and marcasite. Still happens even in controlled environments. Probably a good idea to keep them away from moisture, though - and acids (like the hydrochloric acid produced by plastic bags and PVC containers, etc.). Not sure that the crumbliness in the pyritized ammonites I'm recalling was pyrite rot, or just the nature of the pyrite replacement.
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gemfeller

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Re: Cutting Ammonites
« Reply #10 on: March 25, 2019, 09:27:24 AM »

I can agree on the marcasite problem.  I have a couple of big rough chunks of Nipomo marcasite in agate.  I pulled them off the shelf recently and they'd mostly crumbled, leaving a strong acid smell -- sulfuric most likely.  The same with some slabs I'd cut from them.

I've cut some stones from the same material and they seem to be stable -- or at least stable for 10- 15 or so years since I cut them. I have no idea why polishing the stuff stabilize it (more or less).  I've noticed the metal in some of my cabs does tend to tarnish.

The most interesting ammonites in my collection are from Germany.  They are pyrite casts in what appears to be limestone.  They've been opened and wire-brushed to bring out the metallic color.  I've had them over 20 years and they're still bright and shiny.  The images show one encased in he host rock; then opened.
Ammonite Cast 3.JPG
*Ammonite Cast 3.JPG (76.79 kB . 400x335 - viewed 294 times)
Ammonite Cast 2.JPG
*Ammonite Cast 2.JPG (86.95 kB . 400x299 - viewed 329 times)
   

 
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irockhound

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Re: Cutting Ammonites
« Reply #11 on: March 25, 2019, 12:04:21 PM »

I am wondering.  I don't think I would put any oil on a pyrite but wonder if sprayed with a thin coat of clear paint if that would effectively seal the surface keeping the moisture out and prolonging some of the more troublesome specimens from the decay.  Obviously I wouldn't be doing this to make a change to the look of the ammonites only to seal them.  I have put baby oil on large Hanksite specimens and it does keep them from decaying from moisture but is terrible when dust settles on the specimen with the coating.
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rocks2dust

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Re: Cutting Ammonites
« Reply #12 on: March 25, 2019, 02:30:15 PM »

The fossil preservation folks have discussed this endlessly. Seems to be that once the condition starts, you can delay, but not stop it. I recall some saying that coating the pyrite with a sealant made the condition worse (presumably by trapping whatever moisture and acidic substances that may be inside). Might have just as good or better results from doing nothing and keeping the piece dry and away from acid environments.
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irockhound

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Re: Cutting Ammonites
« Reply #13 on: March 25, 2019, 08:02:14 PM »

I'd agree on not coating after it starts just like painting over a rusted car, it's too late.  I would only try sealing before it starts or not bother.
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ileney

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Re: Cutting Ammonites
« Reply #14 on: March 27, 2019, 11:31:33 AM »

I have a couple of pyrite specimens that are pretty large by comparison - a few inches each. One is a sand dollar fossil. I live on the coast and have been keeping the heavy, larger one on display on the kitchen windowsill on top of the sink, having never heard of this decay. I haven’t noticed any change. Of course. Now I will have to check carefully when I get home after reading this.
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