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[vitzitziltecpatl]

Those are indeed the definitions of synthetic/simulant/natural materials.

Unfortunately, VegasJames, most people will never bother to learn about these sorts of things. Bugs me sometimes, too.

One of the funniest things I've ever seen was a big-box jewelry dep't sign in a case with their "Genuine Lab Created Opal"... .

[R.U. Sirius]

I appreciate the nuance of synthetic vs. simulant, but I find it irrelevant in practice - be it for the consumer, or for the artist. Laboratory-grown materials are of course different from naturally occurring materials in many practical ways, (cost, consistency in properties, dependance on proprietary processes), and should be disclosed as such.

The synthetic vs. mere simulant distinction, however, depends on how hard we look, and how much we are willing to spend on instruments. Naked eye, loupe, microscope, refractometer, Raman spectrophotometer, FT-IR, electron microscope, trace element analysis, isotope analysis, XRD - eventually, you will find a difference, no matter how small, between the synthetic and the natural material, and thus the "synthetic" will suddenly become the "simulant". There is no objective distinction between the two categories, it simply depends on our technical ability. All lab-grown materials are either simulants, or completely novel materials that never aimed to simulate a natural material (goldstone, for example).

[VegasJames]

I appreciate the nuance of synthetic vs. simulant, but I find it irrelevant in practice - be it for the consumer, or for the artist. Laboratory-grown materials are of course different from naturally occurring materials in many practical ways, (cost, consistency in properties, dependance on proprietary processes), and should be disclosed as such.

The synthetic vs. mere simulant distinction, however, depends on how hard we look, and how much we are willing to spend on instruments. Naked eye, loupe, microscope, refractometer, Raman spectrophotometer, FT-IR, electron microscope, trace element analysis, isotope analysis, XRD - eventually, you will find a difference, no matter how small, between the synthetic and the natural material, and thus the "synthetic" will suddenly become the "simulant". There is no objective distinction between the two categories, it simply depends on our technical ability. All lab-grown materials are either simulants, or completely novel materials that never aimed to simulate a natural material (goldstone, for example).

Again I disagree. The definition of synthetic when it comes to stones is having the same chemical makeup but being artificially made. Therefore, a synthetic ruby/sapphire is still a synthetic regardless if it has the same crystal structure or refractive index.  For instance, flame fusion rubies are cooled so rapidly that they do not form much of a crystal structure unlike flux or hydrothermal grown rubies. Yet all three forms of rubies are still synthetics.

Simulants on the other hand have the look of a particular stone but not the chemistry. For example, red glass can, which is silicon dioxide, not the aluminum oxide of ruby/sapphire, could be used as a ruby simulant as it has the look but not exact chemistry of ruby. Plastics made to look like opal would be opal simulants, not opal. By the same reasoning, synthetic opal would have to contain a percentage of water as part of its chemistry to be considered synthetic. Otherwise, it is more like a glass, especially if fused by heat, and thus would be an opal simulant.

[R.U. Sirius]

Got it - the distinction is in chemical composition and crystal structure (ignoring trace impurities, isotopes, inclusions, crystal growth patterns, etc.).

[VegasJames]

Got it - the distinction is in chemical composition and crystal structure (ignoring trace impurities, isotopes, inclusions, crystal growth patterns, etc.).

How can trace impurities be ignored when they can define a stone? For example, ruby and sapphire are both aluminum oxide. In fact, rub is just red sapphire. The name of the stone depends on the color due to trace impurities. Same with things like variscite and turquoise, and others which are aluminum phosphates. They are still different stones bases on trace impurities present. And what about the different forms of quartz such as amethyst and citrine, which are named due to their trace impurities that can give them different colors. Same with the beryls such as emerald, red beryl, aquamarine, maxixe, heliodor, etc. that are all separated by their trace impurities.

[R.U. Sirius]

Right, that's exactly why I originally stated that you can always, in principle, distinguish between lab-grown and natural stones - it's just a matter of how hard you look, with what precision, and with how many analytical techniques. Therefore, the claim that "synthetic stones are identical to natural counterparts in chemical composition" is a moot point - I guarantee that, eventually, I will be able to find a difference in trace elements, isotopes, etc.

We stray far from the original topic here, and it doesn't really matter, as long as we know what someone is frying to say when they say "synthetic" or "simulant" - but my point is that one shouldn't have strong opinion, as synthetics will never be truly "indistinguishable" from the natural material.

[VegasJames]

Right, that's exactly why I originally stated that you can always, in principle, distinguish between lab-grown and natural stones - it's just a matter of how hard you look, with what precision, and with how many analytical techniques. Therefore, the claim that "synthetic stones are identical to natural counterparts in chemical composition" is a moot point - I guarantee that, eventually, I will be able to find a difference in trace elements, isotopes, etc.

We stray far from the original topic here, and it doesn't really matter, as long as we know what someone is frying to say when they say "synthetic" or "simulant" - but my point is that one shouldn't have strong opinion, as synthetics will never be truly "indistinguishable" from the natural material.

We can find all sorts of differences in the same types of various natural stones. Diamonds can have different crystal structures different impurities, and can even have vacancies in the crystal lattice.  Beryls, calcite and various other stones can have various crystal structures. I have found various forms of gypsum as selenite, satin spar, and alabaster in numerous different crystal structures and in various colors (white, red, blue, green, golden, tan, dark brown). And not all stones have crystal structure. There are around 300 types of opal, most of which are completely amorphous. Therefore, crystal structure is pretty much irrelevant. Although, Len Cram I mentioned earlier is producing precious opal that cannot be distinguished from naturally occurring opal.

Opal can also vary a lot in chemistry. Even though all opal contains amorphous silicon dioxide and water, it can also contain a lot of other things. These include crystalline silica, aluminum oxide, uranium, cinnabar, sodium, potassium, carbon, lithium, cobalt, thorium, iron, magnesium, barium, titanium, vanadium, copper, manganese, zinc, nickel, etc.

So getting back to my original point, a synthetic is not based on impurities or crystal structure. A synthetic is a stone that has the same chemistry and form as the base stone. As where a simulant is not the same as an synthetic. A simulant is a substance that has the appearance of the real thing, but without the same chemistry. Therefore, your claim of "eventually, you will find a difference, no matter how small, between the synthetic and the natural material, and thus the "synthetic" will suddenly become the "simulant". There is no objective distinction between the two categories," is incorrect. If we go by your definition then we would have to conclude that amethyst and citrine are quartz simulants since they differ compared to a natural pure quartz crystal.

[irockhound]

I agree and think that is the best description of the differences between simulant and synthetic materials.