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NEWS Latest up - date March 2010 Recent additions or amendments Principal Gemstones; Two new pages have been added to the site. These are DIAMOND (Cape Series )and CHRYSOBERYL (Yellow Brown and Green) To view these pages go to the SPECTRA DATABASE and follow the links in the column on the left. Next one in preparation is Blue and Green Spinel
Through my spectroscope March 2010
BNX0980. Xenotime crystal from Pakistan
ώ - the ordinary ray vibrating at right angles to the "C" axis
ε- the extraordinary ray vibrating parallel to the "C" axis As you can see the above somewhat unattractive brown crystal produced one of the most outstanding rare earth spectra I have seen. The material is of interest mainly to the spectra enthusiast or to the mineral collector. This yttrium phosphate often contains small traces of cerium, erbium and thorium which are probably responsible for the striking spectrum. If you can observe it's spectrum do so while rotating a polarising filter and watch certain lines dance from side to side, as each of the two vibration directions come into line, according to the tetragonal symmetry. These spectra are the "Colour signature" of this particular specimen but may be seen to some degree in other samples of Xenotime. A note to students of the International School of Gemmology San Antonio USA Thank you for your encouraging remarks on this web site. I hope you find the content of some assistance with your studies.
Previous Entry January 2010 Recent additions or amendments Website This is the new look to my web site and I hope you find it viewer friendly and simple to navigate. Spectra Database Principal Gemstones; Three new pages have been added to the site. These are GREEN JADEITE, SYN. BLUE SPINEL & COBALT GLASS and SYN. COLOUR CHANGE CORUNDUM. To view these pages go to the SPECTRA DATABASE and follow the links in the column on the left. Colour Filters; This is a new section which is undergoing construction consisting of various colour filters used in gem testing. Details and images of these filters and their spectra will be included with spectra of gemstones associated with their use. Hopefully this will be uploaded in the near future if I can find a 25 hour day. Orange Gemstones; This is the next section to be added to the Gemstone Comparison Spectra. Several images are ready to build another Excel file but again that rare commodity - TIME - seems to elude me. So watch out for gems such as Spessartine Garnet and the rare gems Bastnaesite and Parisite. Through my spectroscope Jan. 2010
A colleague of mine described this as "Beautiful" and I then that realised that most spectra are. I was so taken up with the technical aspects of spectroscopy that I had missed the obvious as so often can happen with our work. This is the diffraction type emission spectrum of a triphosphor fluorescent tube commonly called an "Energy saving lamp" Have a look with your spectroscope and enjoy the spectacular view. The brightest line in the orange lies at 611nm. The one in the deep violet at 405nm. has been captured by the digital camera but you may not be able to resolve it by eye. Some of my colleagues say they can see it but I can't - Perhaps it's something to do with age? Have fun while you can! And finally my best wishes go to all my viewers for a prosperous and healthy New Year in 2010 Previous Entry November 2009 Recent additions or amendments Spectra Database Now that Gem - A have decided to present gemstone spectra to read 400nm. on the left in their gemmology course notes I have amended my images accordingly. My poor confused brain is gradually adjusting after more than half a century using my spectroscope in the reverse direction. The pages of my spectra database compiled so far now show both versions of spectra 400-700nm. and 700-400nm. This will continue for a limited period and will gradually be phased out, as it increases the work load considerably. I have also recently converted my spectra of the commercially important principal gemstones to read 400- 700nm. which is what our future students will come to expect. Gemstone Comparison Spectra Colourless gemstones; A better image of the garnet top doublet in CS1. now shows the thin slice of garnet on the table facet. Red gemstones; Chondrodite and Epidote have bee added to RD1.and Tourmaline has been added to RD4. Pink gemstones; Three pink groups have been added to the database. Principal Gemstone Spectra Alexandrite; I have at last managed to capture the fluorescing emission doublet in the red on camera. This synthetic stone is remarkably similar in colour both in daylight and tungsten light to synthetic colour change corundum so beware not to rely on appearance alone. Through my spectroscope Nov. 2009
Now what do think this one might be? It's what you might see if you are holding a gemstone in your fingers while you search for a spectrum. Stray light enters your spectroscope which has transmitted through the edge of your skin. Yes it's blood, not just any old blood but my last drop sweated for you in the service of gemmology.
Gem - A Conference London October 2009 Life's full of surprises - nobody tells me anything! I felt very honoured to be presented with the "R. Keith Mitchell Award for Gemmological Spectroscopy" and I thank all those who thought me worthy of this achievement. It was good to meet friends and colleagues again and I hope those who attended my workshop found some inspiration to further their expertise in the use of the spectroscope. Thanks to all for your courtesy to Kathleen and myself in the magnificent setting of Goldsmiths Hall
John and Kathleen Harris.
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