Aha! the old heat conductivity test!
Here’s a commercial link to some interesting info about the differences between diamonds and cz.
Something like that.
Debeers is pretty much a case study for cartels (google Debeers Cartel), though lately they’ve been undermined by some coming out of Russia and Canada.
The cold, hard truth is that there’s blood on a lot of the products we desire so strongly. That may include CZs, but definately includes oil, tobacco, clothing, and shoes to name just a few.
The question is, how far do we distance ourselves so that we can have what we want without guilt attacks.
Me? I’d prefer a CZ and a two or three week cruise. In 1st class.
They give you chocolate, moon. All you can eat. 
No mustard?
Not all of us, TexasSpur. I want a sapphire again, should I be lucky enough to get engaged again.
Real, or fake?
And how will you know?
Well, if it’s fake but looks good, I wouldn’t mind, since I intend to be along picking it out!
Of course, you could always get Moissanite, which has an even higher RI than diamond - 2.65 IIRC, and it is nearly as hard as diamond as well.
Yes. It’s called Moissanite, and it is indistinguishable from diamond in every respect, even to trained experts with the best optical tools. The test?
Moissanite floats.
That’s it. At about half the cost of a diamond and flawless every time, it’s a good facsimile of the real thing. (Just don’t let your woman find out.)
Floats on what? Every source I can find quotes the density of moissanite at 3.21 gcm[sup]-3[/sup]. Water is 1.00. Diamond is 3.52.
It’s not completely straightforward – he can tell diamond and CZ apart, but when presented with three identical stones which he is nearly-certain are diamonds, he has to choose between
- admitting his assessment was wrong (relatively easy),
or - being dumbstruck by the incredible odds against three such diamonds existing.
The truth is neither (1) nor (2), but that the diamonds are artificial and will eventually destroy the DeBeers cartel.