Ammolite ?

[John Papastathis]

Hi folks,

I recently acquired this beautiful little 3-1/2"x 3-1/2" plate from a rock shop in North Jersey. At first I thought the ammonites were pyritized but the shop owner said it was "opalized". Looking on the web I am now guessing it is ammolite; the gemstone composed mainly of aragonite(main material in mother-of-pearl) with a good amount of pyrite thown in the mix. I'm guessing this because of the colors and irredescence. Also, she said it was from Russia. Any ideas ?

[geofossil]

Not really. I have to put on my geologist hat. Ammolite is a 'specific' recognized mineral from here in Alberta. The refractive index is measured via sodium light, 589.3 nm is as follows: α 1.522; β 1.672–1.673; γ 1.676–1.679; biaxial negative. There are quite a few elements making up 'ammolite' other than the original arragonite and pyrite.

Having said that your specimen may be similar and have many of the same qualities but is unlikely to be ammolite. It doesn't make your specimen less interesting or collectable. It's a bit like wine: a true 'Bordeaux' comes from that region of France and it can't be copied...but a wine from elsewhere might be every bit as good but is never exactly like a Bordeaux because of soil, etc.

[John Papastathis]

Thanks very much for the information. I would rather know that I am wrong than be calling something something other than it really is. However, what would you call it ? Might it have a specific classification or should I just refer to it as opalized/pyritized or ammolite-like. Any input would be appeciated.

Thanks,

John

[geofossil]

Thanks very much for the information. I would rather know that I am wrong than be calling something something other than it really is. However, what would you call it ? Might it have a specific classification or should I just refer to it as opalized/pyritized or ammolite-like. Any input would be appeciated.

Thanks,

John

Is your specimen coated with an acrylic or anything to enhance or protect the finish? If not (and hopefully not) then it isn't ammolite-like. I'm over my head here but opals and ammolite are capped with refractive coating that acts as a lens. My wife has a ring with an ammolite setting. You specimen might actually be more natural and thus have more interest as a fossil as well as a piece of art.

Here's an uncoated edge of an Alberta ammonite, Placenticeras meeki, giving the colour:

[PaleoRon]

It is definitely not opalized. That is a term some dealers use to make the piece seem more valuable than it would otherwise be. In order to be opalized the piece must be replaced by / or made of opal. One term that is commonly used to describe a play of colors is Opalescent, which does not mean something is made of opal. Some modern shells display opalescence when polished. A good example is polished abalone shell.

[John Papastathis]

How would I know if it's coated ? Should I scratch a small section ? Under UV light it displays a grayish-green cast. On closer examination the photo doesn't accurately show the colours. There is alot more green in it like in the Alberta pic you've added.

John

Ps;

Thanks again for the correction on the "euryptid". It will be disappointing to tell my friend it's not a fossil. However, it makes it alot easier on me to give it back to him now !

[Ricky Suave]

This is a Psiloceras Planorbis. This species dates to the Jurassic and comes from Blue lias, Somerset England. The specimen is made of ammolite, a gem stone, the same one that is found in meekis.

[Harry Pristis]

This is a Psiloceras Planorbis. This species dates to the Jurassic and comes from Blue lias, Somerset England. The specimen is made of ammolite, a gem stone, the same one that is found in meekis.

'Ricky Suave' has it. That is a nice double. Here is my example.

[ammofan]

HI JUST THOUGHT I WOULD ADD AN EXTRA NOTE, WHAT YOU ARE SAYING IS CORRECT RE THE AMMONITE AND WHERE IT WAS FOUND, BUT THE PRESERVATION OF THE SHELL IS NOT ACTUALLY CALLED AMMOLITE ON THE ENGLISH AMMONITE, THE NAME AMMOLITE IS ONLY RESERVED FOR THE PLACENTICERAS SPECIES OF AMMONITES FROM THE STATES AND CANADA, AS THIS IS A REGISTERD DESCRIPTION FOR THAT SPECIES ONLY. THANKS CARLO

[tracer]

this is kinda like some of the debates over shark teeth. first you have to define your terms. i consider ammolite to be only the stuff from the placenticeras fossils in that one area of northernness above and west of the masons and the dixons and their lines. but the composition of ammolite is somewhat variable (duh), so it in my mind to a degree defies exact definition, mineraliologically keyboarding )i'm not speaking(.

that stuff from over yon large wetness is, from the looks of it, more pyritized than anything. but regardless, a key point is that ammolite aren't opalized. a broader key point is that all that's shiney and colorful aren't the same thing. if i were to polish my jester's cap, i'd still just be a shiney fool and you couldn't sell me for squat. (what's that old saying about a pig's purse being made of silk?)

in closing, i'd like to say that my hypothefact here shouldn't irritantrum anybroady who'd already gotten a notion lodged sideways on this issue because - #1. i din't say nothing about anybody's shark teeth being no kin to megs. #2. i din't assert that anyone's favorite mineral was uninvolved. and #3. everybody's now got the perfect excuse to tell their significant neither that they have to go buy one of each type of shiney colorfulnessitude on the planet.

have a great month.