[Rockhounds] Scapolite again

[Steve Sellepack]

Based on the below discussion the problem may have a computational solution.
As fluorescence is a band structure property the influence of the concentration of the specific element in a specific site will be displayed in the band structure.  Computational modeling of the band structure correlating to the site replacement may not display an energy gap equal to a red fluorescence but modeling of the series should display enough of a band gap shift to be able to correlate the properties from natural specimens to concentrations of iron or aluminum in the T2 sites.   
Steve

-----Original Message-----
From: "Axel Emmermann" [axel.emmermann at pandora.be]
Date: 10/03/2008 07:54 PM
To: "'Rockhounds at drizzle.com: A mailing list for rock and gem collectors'" 
Subject: RE: [Rockhounds] Scapolite again

> > I don't see a direct connection with what I'm looking for but I would be
> > inclined to think that it might be rewarding to compare meionite
specimens
> > coming from really big, slow cooling intrusions with those from smaller
> > metamorphic regions.
> 
> 
> Now you're thinking like a mineralogist. 

[Axel] I try ;-)))
It's real hard to peer into these really complicated structural issues but
when you take the time and effort it becomes somewhat less cryptic and more
down to earth.


>I still can't predict the
> answer, but your course of investigation would be on the right track.

[Axel] I'm going to pursue this. Perhaps a few people with lab-access can
help me get some answers. Ultimately I'd like to know what causes the red
fluorescence. My bet is on Fe3+ replacing Al3+ in the T2 sites. But wild
guesses are like wild geese... It's hunting season (LOL).

> Given enough time, structures will seek to resolve into the most stable
> coordination scheme, with the lowest potential energy (in general).

[Axel] I'm doing something (by trial and error) with tungsten carbide at
work. Funny stuff that responds weirdly to annealing. If you heat it to 450°
C slowly and let it cool slowly, it gets oxidized and you get a blue
iridescent surface film. If you heat it quickly, it tends to become brittle.
But if you heat it slowly and cool rapidly, it regains its metallic lustre.
It goes to show that crystals and annealing are closely correlated.

Take care
Axel 



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