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Help with synthetic

Posted by John Lichtenberger  
avatar Help with synthetic
June 19, 2012 01:04AM
We have some synthetic material my wife cut that looks alot like CZ, EXCEPT for the following...

Hardness is in the 5 to 6 range... (CZ is 8-8.5 Mohs)

Relative Density is 6.22 - 6.24 (no less, multiple measurements) (CZ is 5.6-6.0

Melting point is ~ 1000 C, roughly red heat (melts at the inner cone of butane mini-torch) to a glassy blob
(CZ is much much higher)

Looks alot like CZ but somewhat less dispersive

Stone is transparent yellow-green, with a yellowish orange flourescence from a LW laser pen



trying to find something else with these properties is somewhat daunting (don't have a refractometer, although I may buy one, or maybe make one)

...but the RI may be too high for a standard tool...

Doubt that it's something exotic, as we got a bunch of it from an estate... but who knows?? maybe one of the syn garnets??

any help appreciated..

John L.



Edited 1 time(s). Last edit at 06/19/2012 01:39AM by John Lichtenberger.
avatar Re: Help with synthetic
June 19, 2012 01:46AM
    
Hi John,

Not to many possibilities here I think. Wild guesses would include some synthetic similar to Scheelite or maybe some Microlite group species. When you find out for sure, let us know. Interesting.

Ron



Edited 1 time(s). Last edit at 06/19/2012 01:48AM by Ronald John Gyllenhammer.
avatar Re: Help with synthetic
June 19, 2012 01:56AM
    
Hi John,

I forgot to ask if you're confident that it is a synthetic for sure.

Ron



Edited 1 time(s). Last edit at 06/19/2012 01:57AM by Ronald John Gyllenhammer.
avatar Re: Help with synthetic
June 19, 2012 03:43AM
Probably not pure scheelite, but could be doped. Natural scheelite typically has a brilliant blue-white fluorescence under shortwave UV, but is barely or nonreactive under longwave UV. A dopant, however, could charge that.
avatar Re: Help with synthetic
June 19, 2012 04:28AM
    
I know that this wouldn't be fluorescent unless something was added to make it fluoresce, and it's not synthetic per se, but what about a type of "lead crystal" ? As you obtained them from an estate sale, have you got an idea how old the stones might be? That might give a clue. As an aside I have some stones that were sold to me as topaz that fluoresce yellow, I am still trying to determine what they are.

edit - RI of leaded glass approx 1.7, less than cz
density can be as high as approx 6, a little under what your calc obtained but close
hardness around 6
working temp up to 1100

Interesting mystery!
regards,
stephanie smiling smiley



Edited 2 time(s). Last edit at 06/19/2012 05:22AM by Stephanie Martin.
avatar Re: Help with synthetic
June 19, 2012 07:44AM
John,
Do you have a polariscope? Is it isotropic or not. If not, can you resolve a uniaxial or biaxial figure?

Rock Currier
Crystals not pistols.
Re: Help with synthetic
June 19, 2012 08:17AM
John,

Rather than continuing the cogitation on this matter, please just send me one that I can keep, and I will provide an x-ray spectrum at no cost other than the stone..

I collect synthetic minerals and sometimes use them in my electron probe reference standard business.

Bart Cannon'
Cannon Microprobe
1041 NE 100th Street
Seattle, WA 98125



Edited 1 time(s). Last edit at 06/19/2012 08:33AM by Bart Cannon.
avatar Re: Help with synthetic
June 19, 2012 01:12PM
There is no good fit for a common synthetic gem at John's observations of SG and hardness sad smiley Feeling in my water is for GGG (Gadolinium Gallium Garnet) rather Synthetic Scheelite but there's no other obvious runner than those two.

GGG is cubic and there is no other cubic and transparent gem crystal anywhere near John's SG. GGG will test as such using just a laptop screen and a pair of Polaroid specs, if John does not have a polariscope.

Scheelite is tetragonal and thus doubly refractive. There is sufficient birefringence for John to see doubling of the back facets under a loupe and with the cut specimen he has. Scheelite A/S in a synthetic specimen should be diagnostic.

Insh'Allah, that does it.
avatar Re: Help with synthetic
June 19, 2012 09:58PM
Bart Cannon Wrote:
-------------------------------------------------------
> John,
>
> Rather than continuing the cogitation on this
> matter, please just send me one that I can keep,
> and I will provide an x-ray spectrum at no cost
> other than the stone..
>
> I collect synthetic minerals and sometimes use
> them in my electron probe reference standard
> business.
>
> Bart Cannon'
> Cannon Microprobe
> 1041 NE 100th Street
> Seattle, WA 98125

That's generous of you Bart. Is a 4.3 gram chip enough of a sample??

Don't think it's GGG, as the RD is too low (6.21-6.23 vs. 7.02-7.09), as is the melting point...

Just measured a 125 carat CRB doorknob and it too measures 6.23 gm/cc... did a reality check on known CZ... 5.9 gm/cc by same method

John L.
Re: Help with synthetic
June 19, 2012 10:04PM
    
Some values also correspond to synthetic strontium titanate.
EMJ
avatar Re: Help with synthetic
June 19, 2012 10:17PM
    
Evan, I was thinking that too, but I think the melting point is way too high...
avatar Re: Help with synthetic
June 19, 2012 11:12PM
Evan Johnson (2) Wrote:
-------------------------------------------------------
> Some values also correspond to synthetic strontium
> titanate.
> EMJ

I though about it, but John says that the dispersion (fire) is less than CZ. just in the hand and under a strong light the fire in a cut Strontium Titanate should be seen as much greater than any CZ. Here's an example.


Secondly, the SG of Strontium Titanate is way off from John's measurement and its reported boundaries are tighter then most (+/- 0.02); CZ is closer. Thirdly. if John has been melting bits in a flame, he should have picked up the distinctive Strontrium flame colouration.

Of all the forms of testing, I think that scratch testing against Mohs's scale is the one most likely to give a poor result (assuming a good balance and hydrostatic weighing rig were used).

Do you have a pic of the rough, John?
Re: Help with synthetic
June 20, 2012 12:15AM
John,

A 4.3 gram sample is adequate.

Typical Strontium Titanate is colorless.

Bart
avatar Re: Help with synthetic
June 20, 2012 12:38AM
These are about as rough as it gets...



Large faceted doorknob at 12 o'clock is 125 carats, partially cut at 9 o'clock... just another BIG doorknob partly cut... (greenish hue due to dop wax), piece at lower center maybe 60 carats or so, shaped like a boule...

here is the cut stone and Barts chip in natural and fluorescent (LW) (bluish color in chip due to lighting, not fluorescence... cut stone shows orang-ish fluorescence due to internal reflections)



Strontium Titanate it isn't... the whole purpose of the flame was to test for strontium, no flame colors at all, but then I said, what the heck, let's see if it melts or decrepitates....melted like glass at red-orange heat...probably in the 1000C to 1400C range at most.



Edited 2 time(s). Last edit at 06/20/2012 12:42AM by John Lichtenberger.
avatar Re: Help with synthetic
June 20, 2012 02:15AM
Allochromatic. Like Corundum, Spinel, CZ etc, it can be doped pretty much any colour so body colour is no guide. But Strontium Titanate with an unusually high dispersion value of 0.190 will show the fire (dispersive colouration) that must come with it, whatever the body colour may be. CZ has the dispersion value of 0.60, Diamond 0.44 and GGG is 0.45. From the pic of John's cut stone, even allowing for using a multiple light source, I'd be surprised very surprised if Scheelite could showed that much fire as is in the pic (dispersion value is 0.026 - similar to Hessonite).

But, as we know, guessing from a pic and partial info may be fun but it's still guessing. Viewing in person and testing with calibrated instruments is the one way to certainty.

......I just checked the melting point of GGG. 1725 deg C Too hot for John's hand-held melting sad smiley

..... And just came across a paper suggesting that the MP for Scheelite mixed crystals with RE, produced for lasering are in the range 690 - 1100 deg C. [arxiv.org]

Better! If it is a mixed Scheelite crystal then the other characteristic properties (SG, dispersion etc, may vary substantially from those for pure Scheelite. etc). It begins to sound as though Bart's XRDF may really show us its paces smiling smiley



Edited 1 time(s). Last edit at 06/20/2012 11:42AM by Owen Lewis (2).
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