Post subject: New Opal (Homogeneously Crystalized)
Posted: Tue Mar 14, 2017 4:46 pm
Established Member
Joined: Wed Nov 09, 2011 5:35 am Posts: 36
Just for your information:
I’m very happy to see that now it is possible to prepare opals without columnar patterns.
These opals with homogeneously crystallized silica particles in a polymer matrix (= HoC-Si-Pol) don’t show a columnar pattern typical for opals grown by sedimentation. With big polygonal crystallites of 2-3 mm these multicolored opal can be produced in big blocks and different body colors.
Post subject: Re: New Opal (Homogeneously Crystalized)
Posted: Mon Mar 20, 2017 7:25 pm
Site Admin
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
Quote:
homogeneously crystallized silica particles in a polymer matrix
By definition, a synthetic gem is a man-made material with essentially the same chemical composition, crystal structure and optical and physical properties as the natural gem material.
I don't think your stone can be called synthetic opal.
I think almost all man-made opal is polymer impregnated. It is one of those odd edge-cases, since natural opal can be polymer impregnated as well in post, and it would still be opal. Opal beads can also crystallize after formation so that isn't necessarily a disqualifying factor either.
I agree though that it is a weird edge case and has some definite differences to natural material. Hopefully that will make for easier identification, given how different this looks from traditional synthetic material.
Just call it artificial. The word synthetic has no meaning relative to value.
That's not true when it comes to opal. Metal foil in glass or resin could look superficially similar in a photo but in person the resemblance is slight.
Post subject: Re: New Opal (Homogeneously Crystalized)
Posted: Wed Mar 22, 2017 5:50 pm
Site Admin
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
I would tend to call these opals an artificial product as well.
Like CZ. Yes, Baddeleyite (ZrO2 occurs naturally, but it never contains the dopants (lower-valence oxides like Ca O, MgO, or Y2O3 which make it crystallize in the cubic system.
Post subject: Re: New Opal (Homogeneously Crystalized)
Posted: Wed Mar 22, 2017 11:44 pm
Valued Contributor
Joined: Sat Nov 05, 2016 11:29 am Posts: 142
I would call it a simulant, as it is not an opal. A synthetic, or lab created opal would largely have the same characteristics as natural opal, which this clearly does NOT, as it is roughly 80% plastic, vs. 20% SiO2, and its specific gravity is horrendously off (much lighter than real opal) ...
Post subject: Re: New Opal (Homogeneously Crystalized)
Posted: Thu Mar 23, 2017 4:40 pm
Site Admin
Joined: Sun Oct 16, 2005 12:22 pm Posts: 21602 Location: San Francisco
This is a professional gemological forum, Goldberg. Yes, as gemologists, mineralogists and chemists we DO want to know what "homogeneously crystallized“ is intended to mean in regards to opal and whether or not it is just a deliberately obfuscating description.
Pretty video on crystalline suspension of colloidal silica particles but what does that have to do with calling a predominately plastic product a synthetic opal?
When they say "colloidal crystal" on the vodeo I believe they are referring to the concept of a photonic crystal (ie an orderly arrangement of particles that diffracts light the way a crystal diffracts xrays). It would be weord to use the term "homogenously crystallized" to refer to that phenomenon. I could see synthetic vs simulant going either way, but we already call other resin-infused products synthetics, and since it is used as a binder for silica particles arranged in the same way as in a natural opal I don't mind it much. One way or another it is quite different from lesser imitations. Seems like the end product might be like taking one of those Ethiopian chalk opals and soaking it with resin. Fortunately that should make distinguishing them relatively easy, which is always a big plus.
Post subject: Re: New Opal (Homogeneously Crystalized)
Posted: Thu Mar 23, 2017 7:58 pm
Gold Member
Joined: Thu Jan 24, 2008 4:01 pm Posts: 1902 Location: Pine City, NY and Dothan, AL
"Homogeneously crystallized“ just means that the nucleation starts within the mix, rather than from the surface. I think this is just another example of using big words to impress potential customers. As for the simulant/synthetic question, I'll leave that to you gemologists It's obviously not natural opal.
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