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Colouration in natural beryls: A spectroscopic investigation

DSpace at IIT Bombay

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Title Colouration in natural beryls: A spectroscopic investigation
 
Creator MATHEW, G
KARANTH, RV
RAO, TKG
DESHPANDE, RS
 
Subject channel constituents
charge-transfer
cordierite
minerals
spectra
beryl
colour
irradiation
heating
electron spin resonance
optical absorption spectroscopy
mossbauer spectroscopy
orissa
 
Description Beryl samples from Badmal mines, Orissa were studied by electron spin resonance, optical absorption and Mossbauer spectroscopy. It was found that on artificial irradiation, colourless beryls from Orissa turned to shades of yellow-green. On subsequent heating at 300 degrees C, the hue changed to yellow and upon further heating at controlled conditions they turned to a more desirable sky blue, accounting for value addition. Continued heating above 500 degrees C, however, rendered them colourless. Similar studies were also carried out on natural yellow, blue and green beryls from Orissa, all of which acquired a greenish hue on irradiation and turned colourless on heating to >5000 degrees C. Electron probe microanalysis of beryls showed iron as the major transition element impurity. ranging in concentration between 0.5 to 0.7wt%. Investigations using electron spin resonance, optical absorption spectroscopy and Mossbauer spectroscopy reveal that: colours produced were on account of Maxixe-type defect centres as well as radiation-induced oxidation of Fe2+ to Fe3+ ion and associated charge transfer process. It is interesting to note that the yellow and blue colour produced on irradiation as well as post irradiation heating showed similar hue to that of the natural ones, both having formed on account of similar charge transfer process. Thus, it can be inferred that natural yellow, blue and green colours in beryls comprising low iron impurities are due to prolonged irradiation in nature.
 
Publisher GEOLOGICAL SOC INDIA
 
Date 2011-07-29T21:52:42Z
2011-12-26T12:52:39Z
2011-12-27T05:39:15Z
2011-07-29T21:52:42Z
2011-12-26T12:52:39Z
2011-12-27T05:39:15Z
2000
 
Type Article
 
Identifier JOURNAL OF THE GEOLOGICAL SOCIETY OF INDIA, 56(3), 285-303
0016-7622
http://dspace.library.iitb.ac.in/xmlui/handle/10054/7844
http://hdl.handle.net/10054/7844
 
Language en