Ammolite vs. Opal

[Cave Keeper]

When I look at Ammolite, I can''t help wondering how does one differentiate between Ammolite and Opal?

Isn''t the geological process which creates the Ammolite shell the same as those that creates Opals, i.e., opalization?

Is there any difference between mother-of-pearl and Ammolite shell?

Does anyone have any idea?

 

[valeria101]

I am not 100% sure of what is the chemistry of ammolite fossils

But structurally these are different than opal and the geology is different as well.

Interesting Q! Never thought of this... It should be a nice afternoon exercise to pull together all things that make opalescence in gems what thee are (diamodns included) and make a comparison. Obviously there is something they have in common to make light behave in the same way. I have no idea of any online refference for this though.

 

[Richard M.]

Hi,

Both precious opal and ammolite owe their play of color (correct term for this phenomenon) to light diffraction (NOT refraction), but for very different reasons. They are chemically very different and the mechanisms for breaking light into spectral colors are different also. Anyone seriously interested in learning about this can go to the following sites and spend a bit of time learning. The opal information is mostly accurate although after many years as an opal cutter I'd dispute a few things in it. There is probably more blatant nonsense in print about precious opal than any other gem but this article is pretty good.

Opal

Ammolite

Richard M.

 

[Cave Keeper]

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On 7/23/2004 1:21:52 PM Richard M. wrote:

:
Both precious opal and ammolite owe their play of color (correct term for this phenomenon) to light diffraction (NOT refraction), but for very different reasons. They are chemically very different and the mechanisms for breaking light into spectral colors are different also.
:
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Hi, thanks for the sourc links and your comments.

I wonder whether the claim that Ammolite is the World's rarest gem is true. Somehow, I have the impression Bixbite is even rarer.

 

[Richard M.]

Actually, my choice for the world's rarest gemstone is grandidierite. This 0.29 carat cut stone is the only one in existence, according to the GIA.

There are many gems more rare than either bixbite or ammolite, so the comment falls into the "marketing hype" area. The writer makes the statement knowing s/he's unlikely to be disputed because there's no genuine way of knowing.

 

[Cave Keeper]

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On 7/23/2004 1:21:52 PM Richard M. wrote:
Hi,
Both precious opal and ammolite owe their play of color (correct term for this phenomenon) to light diffraction (NOT refraction), but for very different reasons. They are chemically very different and the mechanisms for breaking light into spectral colors are different also.
:
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I thought both opal and ammolite have spherule surface material. So how is it the mechanisms for breaking light into spectral colors are different?

Do the colors in opal change accordingly when its surface is rotated as is possible in ammolite? I think this iridescence process is called spectrochromatic shift.

 

[Richard M.]

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On 7/25/2004 8:25:38 AM Cave Keeper wrote:

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I thought both opal and ammolite have spherule surface material. So how is it the mechanisms for breaking light into spectral colors are different?

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Re-read the section on Iridescence in the Ammolite link. There's a big difference between spherules and platelets.