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Identity HelpHelp with synthetic

19th Jun 2012 02:04 UTCJohn Lichtenberger

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

http://i3.photobucket.com/albums/y62/auplater/fluorite.jpg

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.

19th Jun 2012 02:46 UTCRonald John Gyllenhammer Expert

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

19th Jun 2012 02:56 UTCRonald John Gyllenhammer Expert

Hi John,

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

Ron

19th Jun 2012 04:43 UTCSteve Hardinger 🌟 Expert

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.

19th Jun 2012 05:28 UTCStephanie Martin

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 :-)

19th Jun 2012 08:44 UTCRock Currier Expert

John,

Do you have a polariscope? Is it isotropic or not. If not, can you resolve a uniaxial or biaxial figure?

19th Jun 2012 09:17 UTCBart Cannon

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

19th Jun 2012 14:12 UTCOwen Lewis

There is no good fit for a common synthetic gem at John's observations of SG and hardness :-( 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.

19th Jun 2012 22:58 UTCJohn Lichtenberger

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.

19th Jun 2012 23:04 UTCEvan Johnson

Some values also correspond to synthetic strontium titanate.

EMJ

19th Jun 2012 23:17 UTCStephanie Martin

Evan, I was thinking that too, but I think the melting point is way too high...

20th Jun 2012 00:12 UTCOwen Lewis

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?

20th Jun 2012 01:15 UTCBart Cannon

John,

A 4.3 gram sample is adequate.

Typical Strontium Titanate is colorless.

Bart

20th Jun 2012 01:38 UTCJohn Lichtenberger

These are about as rough as it gets...
http://i3.photobucket.com/albums/y62/auplater/unk01.jpg
http://i3.photobucket.com/albums/y62/auplater/unk02.jpg

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)
http://i3.photobucket.com/albums/y62/auplater/IMG_0968.jpg
http://i3.photobucket.com/albums/y62/auplater/IMG_0967.jpg

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.

20th Jun 2012 03:15 UTCOwen Lewis

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 :-(

..... 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. http://arxiv.org/pdf/0902.1413.pdf

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 :-)

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