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Physics and Chemistry of Minerals

, Volume 42, Issue 4, pp 287–302 | Cite as

Optical and crystal-chemical changes in aquamarines and yellow beryls from Thanh Hoa province, Vietnam induced by heat treatment

  • Jana FridrichováEmail author
  • Peter Bačík
  • Petra Rusinová
  • Peter Antal
  • Radek Škoda
  • Valéria Bizovská
  • Marcel Miglierini
Original Paper

Abstract

Optical and crystal-chemical changes in two beryl varieties after the heat treatment were determined using a wide spectrum of analytical methods. Studied aquamarines are generally more enriched in Fe (up to 0.25 apfu) and alkali (up to 0.08 apfu) than yellow beryls (up to 0.07 apfu Fe, up to 0.04 apfu alkali). The determined c/a ratio of 0.997–0.998 classified all our studied beryls as “normal” beryls. While no crystal structure changes were observed in samples heated to 700 °C, those heated to 900 and 1,100 °C exhibited cracks and fissures. Reduced Fe occurred in samples heated between 300 and 700 °C, and subsequent oxidation from 900 to 1,100 °C induced changes in their colour and clarity. The Fe-bearing beryl colour is controlled by the position of the absorption edge and the presence of a broad band attributed to Fe2+ in the NIR region. Blue colour results from the absorption edge located deeper in the UV region and the presence of broad band in the NIR region. Shift of absorption edge to the visible region at the presence of the broad band gives a yellow colour. Although our studied beryls are enriched in H2O I molecule due to their low alkali content, the H2O II molecule is also present. The following two dehydration processes were observed: (1) release of one double-coordinating H2O II molecule at 300–500 °C and (2) total dehydration at 900–1,100 °C. The observed cracks and fissures likely resulted from channel water release in large beryl crystals.

Keywords

Beryl Heat treatment Powder X-ray diffraction Infrared spectroscopy Mössbauer spectroscopy Electron microprobe UV/Vis/NIR spectroscopy Raman spectroscopy 

Notes

Acknowledgments

We thank C. McCammon for editorial handling and J. Fukuda and A. Ertl for their detailed reviews and very useful suggestions. We also thank Ray Marshall for language review of the manuscript. This work was supported by projects APVV-VVCE-0033-07 (P.B., J.F., P.R.), APVV-0081-10 (P.B., J.F., P.R.), VEGA-1/0255/11 (P.B., J.F., P.R.), CZ.1.05/2.1.00/03.0058 (M.M.) and CZ.1.07/2.3.00/20.0155 (M.M.).

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Jana Fridrichová
    • 1
    Email author
  • Peter Bačík
    • 1
  • Petra Rusinová
    • 1
  • Peter Antal
    • 2
  • Radek Škoda
    • 3
  • Valéria Bizovská
    • 4
  • Marcel Miglierini
    • 5
    • 6
  1. 1.Department of Mineralogy and Petrology, Faculty of Natural SciencesComenius University in BratislavaBratislavaSlovak Republic
  2. 2.Department of Inorganic Chemistry, Faculty of Natural SciencesComenius University in BratislavaBratislavaSlovak Republic
  3. 3.Department of Geological SciencesMasaryk UniversityBrnoCzech Republic
  4. 4.Institute of Inorganic ChemistrySlovak Academy of SciencesBratislava 45Slovak Republic
  5. 5.Department of Nuclear Physics and Technology, Faculty of Electrical Engineering and Information TechnologySlovak University of TechnologyBratislavaSlovak Republic
  6. 6.Faculty of Science, Regional Centre of Advanced Technologies and MaterialsPalacky UniversityOlomoucCzech Republic

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