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 Post subject: beryls
PostPosted: Fri Jun 13, 2008 4:43 pm 
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Ok, John wanted to see what the IR region of beryls looks like. So here are some VIS-IR transmission spectra of beryls. Make of them what you will.

A reminder... when the curve seen in the graph is vertically higher, it means a larger fraction of light with that wavelength is transmitted through the stone. When the curve is lower, more light is being absorbed. Sharp, narrow dips in the spectrum are "absorption lines".

First stone is a yellow beryl that certainly fits the description of Heliodor. (Click on the icon to call up a full scale picture)

Image

Right off the bat, you can tell this is yellow, because the peak transmission in the visible region (400-700 nm) is around 600 nm.

Of the three beryls I looked at, this stone exhibited the strongest absorption lines throughout. Along with the three labeled absorption lines (one in the visible violet, the other two in the IR), there are some smaller lines throughout the IR.


Second stone is an aquamarine that definitely tends toward the blue.

Image

You can tell it is going to be blue because of the peak transmission throughout the 450 nm region.

The labeled absorption lines appearing in the heliodor also appear in this stone, but the IR lines are much weaker here.


Third stone is an aquamarine that tends to look more green than blue.

Image

Again, the green color is apparent with peak transmission around the 550 nm range. Here we have a divot taken out of the transmission spectrum at 600 nm, or else this stone might have looked yellow!

Interestingly, the IR absorption lines seen in the other two stones are missing here.

So, who can tell me what the absorption line at 428 nm ithat appears in all the beryls s due to?


Last edited by Brian on Wed Apr 29, 2009 11:48 am, edited 1 time in total.

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PostPosted: Thu Jun 26, 2008 4:00 am 
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re: 428nm band: Octahederal Fe3+ ?? Read about it here page 4

That 956nm line is the one I saw on the video cam version of the spectroscope unit that kassoy had.

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PostPosted: Thu Jun 26, 2008 8:47 am 
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I would imagine you are correct about the absorption in the blue... usually anything in that range is associated with iron. Probably iron absorption in the recent hiddenite spectrum too, as Spauwe notes.

Checking the emerald spectra I recorded (posted here) and scrolling down to find the spectrum that extends to 1000 nm, the same absorption line at 956 nm appears there. In that thread, Gemça states it is a feature common to beryls. I guess it is almost diagnostic.


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