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PostPosted: Mon May 11, 2009 4:16 pm 
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Well that's surprising! If it is indeed green grossular coloured by chromium occuring in Queensland we'll have a nomenclature problem on our hands again...

Aussie tsavorite :D

Sure will sell quicker!

I'll get some normal data on the stuff ( I lied when I said the RI was too high for me to measure I just never got around to polish a piece so I could take a reading 8) ).

Gimme an hour.


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PostPosted: Mon May 11, 2009 4:43 pm 
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Doesn't look a pretty enough green to be tsavorite, does it.


Last edited by Brian on Fri Oct 02, 2009 1:03 am, edited 1 time in total.

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PostPosted: Mon May 11, 2009 5:19 pm 
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Doesn't look a pretty enough green to be tsavorite, does it

The pieces I sent you don't ey :wink:

Unfortunately the ones I have here don't either...

BTW demantoid is colored by chromium as well. Must have been confused when I wrote that bit on only green grossular retrieving their green by Cr3+. But... to give the beast a name conventional gemology may do the trick:

One takes, a few unknown green garnets and the appropriate literature:

Image

a polishing lap and refractometer,

light and an eye. and this will result in a number: 1.782

This number results in a heap of debate about what to call it exactly. Right into the grey area... Fact is that it's a mix of the two: grossular and andradite. Percentages of elements present don't really interest me at this point. This thread is about spectra.

I was kinda convinced that there wasn't any chromium in there... no spectrum to show for it and I did look at 'm once before through the CCF. Green...

But now Brian's laser is telling us otherwise... Let's dig up that CCF again! Chasing off the spiders that made it its home I had a look again under the 15w daylight fluro's that are hanging underneath my dazor: green... Hmmm... laser = high intensity light.... so... 150W fiber optic on it... hey! Pink!


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PostPosted: Mon May 11, 2009 6:08 pm 
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Tim wrote:
BTW demantoid is colored by chromium as well. Must have been confused when I wrote that bit on only green grossular retrieving their green by Cr3+.


Well rats!


Last edited by Brian on Fri Oct 02, 2009 1:04 am, edited 1 time in total.

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PostPosted: Mon May 11, 2009 6:17 pm 
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What are all those lines!


:shock: Good question!

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All the lines in one spectrum match up with those in the other spectrum. Tomorrow maybe I'll have to put the almandine and hessonite in front of the 514 nm laser.


I expect a flat line but who knows...

How does one get a scholarship to come and play with big-daddy-argon lasers with you? 8)


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PostPosted: Mon May 11, 2009 7:45 pm 
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Tim wrote:
I expect a flat line but who knows...


Probably not... they don't all come from chromium. Best case scenario is that all but the 694 line appear. Worst case scenario is that all the lines appear.

Tim wrote:
How does one get a scholarship to come and play with big-daddy-argon lasers with you? 8)


I don't know. All our new-student scholarships go to recent high school graduates.


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PostPosted: Mon May 11, 2009 9:25 pm 
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I'd have to say all those lines would be a photo luminescent reaction to the 514 laser.....and also that you are basically looking at a raman spectra vs. that of your typical emission/absorption readings, yes?

While the 694nm emission is typical of a Cr XM in corundum, from what I have seen in garnets, the Cr finds itself emitting @ 685nm.

____
bear


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PostPosted: Mon May 11, 2009 10:46 pm 
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Ok, I finally figured out what was going on here. Sadly, it is a problem with the experiment. The lines showing up in these spectra are contamination fluorescence due to Blu-Tack!!

I use a little spot of Blu-Tack at the base of each stone to hold it in place. The straight-line path of the laser beam through the stone is nowhere near this spot. But the laser is very intense, and the stone scatters some of the light, so that every region of the entire stone is flooded with laser light. Unfortunately, as I just found out, the Blu-Tack fluoresces rather easily. It only takes a little of this laser light scattered throughout the gem, and hitting the spot of Blu-Tack, and the Blu-Tack emits a measureable fluorescence.

I just collected a fluorescence spectrum of Blu-Tack all by itself, and most all the lines seen in its spectrum match up perfectly with lines seen in the spectra above.

So no mysterious Raman scattering process, no gem fluorescence. Just contamination fluorescence from the Blu-Tack. What a shame... Blu-Tack is so darn useful. And worse... I have to make sure I clean the stuff out of every nook and cranny of the rough stones, or else these lines will show right back up.


Last edited by Brian on Sat May 23, 2009 3:54 pm, edited 1 time in total.

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PostPosted: Tue May 12, 2009 5:00 pm 
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Found a big peak myself:

Image

threads like these are the greatest! Learn as you go...

I have one question:

how can that 694nm peak with the 532nm laser be so big compared to the other little bumps where when hit with big daddy it is one of the smaller ones?


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PostPosted: Tue May 12, 2009 5:42 pm 
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Well Tim... nice graph. To answer your question, first I have to explain the mistake I was making. :P The answer will (sort of) come at the end of section 1.
Ok, I finally figured out what was going on here. Sadly, it is a problem with the experiment. The lines showing up in these spectra are contamination fluorescence due to Blu-Tack!!

I use a little spot of Blu-Tack at the base of each stone to hold it in place. The straight-line path of the laser beam through the stone is nowhere near this spot. But the laser is very intense, and the stone scatters some of the light, so that every region of the entire stone is flooded with laser light. Unfortunately, as I just found out, the Blu-Tack fluoresces rather easily. It only takes a little of this laser light scattered throughout the gem, and hitting the spot of Blu-Tack, and the Blu-Tack emits a measureable fluorescence.

I just collected a fluorescence spectrum of Blu-Tack all by itself, and most all the lines seen in its spectrum match up perfectly with lines seen in the spectra above.

So no mysterious Raman scattering process, no gem fluorescence. Just contamination fluorescence from the Blu-Tack. What a shame... Blu-Tack is so darn useful. And worse... I have to make sure I clean the stuff out of every nook and cranny of the rough stones, or else these lines will show right back up.


Last edited by Brian on Sat May 23, 2009 3:55 pm, edited 1 time in total.

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PostPosted: Tue May 12, 2009 6:05 pm 
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So now see Tim, I've learned something too.


what a useful board this is!

What I find funny: when hit with 150W white light those grossular -andradites DO give a pink/red reaction through the CCF thus indicating the presence of chromium (cause it isn't cobalt in there I think). The iron that makes these garnets part andradite just mucks up the fluorescence so heavily that it's hard to detect. Even for advanced equipment!

Correct? :o


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PostPosted: Tue May 12, 2009 7:20 pm 
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Blah, more useless information.


Last edited by Brian on Sat May 23, 2009 3:56 pm, edited 1 time in total.

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PostPosted: Wed May 13, 2009 1:53 pm 
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So, I cropped the graph of the didymium glass spectrum that Gene provided to 400 through 700nm and placed it above the spectrum photo of the Zandrite.

Don't ask me why, I just had to. :)

Pretty good match.

Image


Carry on.


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PostPosted: Wed May 13, 2009 3:44 pm 
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JB, I think from now on we'll have to start a new forum rule:

if you publish spectra graphs here you will have to add a spectroscope image of it benath it at scale. The spectroscope image may be a photoshopped image of what you see but can't capture (cause quite frankly, I don't know how you get your camera to pick it up mate... zero succes here :x )

let's provide a spectrum template:

Image


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PostPosted: Thu May 14, 2009 1:19 am 
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When people see an absorption graph like JB posted, I'm always a bit surprised that their mind's eye doesn't automatically construct an idealized version of his photograph. For example, when I look at that graph, I know right away that I won't see any yellow. Just goes to show that I've spent far too much time pinning rainbows to wavelength scales.

Not that I even like absorption graphs, which say to me "here is where you add grey and black." I much prefer the upside-down version, the transmission graphs, which say to me "here is where you reduce color."

And speaking of graphs... Tim, I was looking at your learning curve again. Looks good over the range between "two days ago" and "today", but "tomorrow" seems quite a shocker.


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