October 27-28—SACRAMENTO, CALIFORNIA: 82nd Annual Gem, Jewelry, Mineral and Rock Show; Sacramento Mineral Society; Sat. 10-5, Sun. 10-4
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 Post subject: 3rd Annual Gemology Lecture at Caltech
PostPosted: Mon Aug 06, 2018 3:18 pm 
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The Los Angeles chapter invites all alumni, industry friends, gemstone enthusiasts and guests to attend this special evening presentation by noted Caltech professor and researcher Dr. George Rossman.

Dr. Rossman is professor of mineralogy at Caltech, where he has been since receiving his Ph.D. in inorganic chemistry there in 1971. His work addresses problems relating to mineral identification, the origin of color in gems and minerals, and the global repository of water in rocks and minerals. He was an invited participant in the White House conference on conflict diamonds and has been a keynote speaker at several international mineralogical and gemological symposiums. Dr. Rossman is a Fellow of the Mineralogical Society of America and the recipient of their inaugural Dana Medal, as well as the recipient of the Richard P. Feynman Prize for Excellence in Teaching at Caltech and the Friedrich-Becke Medal from the Austrian Mineralogical Society. He is author or co-author of more than 320 articles in the mineralogical and chemical sciences. Additionally, Professor Rossman received the ultimate honor when in 1998, The International Mineralogical Association named a new mineral - Rossmanite – in recognition for his work on the spectroscopy of the tourmaline-group minerals (and many other mineral species). Dr. Rossman served as a member of the GIA Board of Governors in the 1990s and 2000s and is currently a member of the editorial review board for GIA’s Gems & Gemology journal.


Date
Wednesday, Aug. 15

Time
6:30 p.m. Buffet dinner in the open courtyard - catered by Stonefire Grill

7:30 p.m. Lecture

9:00 p.m. Conclusion

Location
California Institute of Technology
Sharp Lecture Hall, Arms Lab Building
1200 E California Blvd
Pasadena, CA 91125
Map

Cost
$35 - Early bird before Aug. 15
$50 - At door
Parking: street parking is available on Wilson Ave., California Blvd. and in all Caltech campus lots (this parking is at no cost) after 5:30 p.m.

Register
Tickets: To attend, please purchase - Online tickets

Questions
Please contact the Los Angeles chapter at GIALAAlumni@gmail.com


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 Post subject: Re: 3rd Annual Gemology Lecture at Caltech
PostPosted: Fri Aug 17, 2018 6:13 pm 
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Fabulous lecture.
Anyone want to take a stab at it?

Why does chromium color rubies red and emeralds green?

Why does the combination of iron and titanium make sapphires blue?


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 Post subject: Re: 3rd Annual Gemology Lecture at Caltech
PostPosted: Fri Aug 17, 2018 6:54 pm 
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The short answers are

Chrome replaces Aluminum in the Ruby XTL producing a strong effect on energy in the distorted octahedral with a strong ligand field that changes the absorption.

Titanium and iron cooperate in an intervalence charge transfer that changes both valence states and so the absorption of the xtl.

Of course these short answers would make for a poor seminar..... :roll:


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 Post subject: Re: 3rd Annual Gemology Lecture at Caltech
PostPosted: Fri Aug 17, 2018 7:01 pm 
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OK, Steve, A+ on ruby...but how about green in emerald?

This was so fascinating. I wish I had a Dr. Rossman clone for home.


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 Post subject: Re: 3rd Annual Gemology Lecture at Caltech
PostPosted: Fri Aug 17, 2018 9:56 pm 
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OOPs forgot the Emerald. But off the top of my head, here goes.

Chrome as a chromophore in Emerald and ruby are actually very similar. The replacement by chromium molecules in the beryl (which does not fit well causing lots of clarity issues). However, the energy is much lower in the Beryl Lingad field cause absorption in different sections of the spectrum and resulting in the blue/green color.

Do I get a star.


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 Post subject: Re: 3rd Annual Gemology Lecture at Caltech
PostPosted: Mon Aug 20, 2018 11:13 pm 
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Yes, I think a star is in order.
George Rossman wrote:
The important thing (to first order) is that the oxygen ions are closer to the Cr in the red minerals than they would be for the green ones.

It takes more energy (light energy) to move the electrons when the have to overcome the repulsion of the negative charge on the closer-in oxygens and that changes the wavelength of light that must be absorbed to move the electrons, and that, in turn, changes the color of the mineral.


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