Abstract
A red spinel, MgAl2O4, from Burma (Myanmar) containing as chromophores ca. 0.5 wt% of each Cr2O3 and V2O3, was sequentially heated for at least 72 h at temperatures ranging from 600 °C to 1,100 °C. The untreated and quenched samples were examined with single-crystal X-ray diffraction (XRD), Raman spectroscopy and photoluminescence spectroscopy. XRD results display a linear decrease of the cell parameter a and a continuous shift of the oxygen coordinate u, u, u at 3 m toward lower values with increasing temperature and associated Mg, Al disorder: T(Mg1-x Al x )M(Al2-x Mg x )O4. The natural spinel has x = 0.157(2) and reaches x = 0.286(4) after quenching from 1,100 °C. In its natural state, M–O and T–O distances are 1.9226(2) and 1.9361(4) Å. With increasing inversion of Mg from the tetrahedrally coordinated T to the octahedrally coordinated M site, M–O distances increase at 1,100 °C to 1.9333(4) Å and T–O distances decrease to 1.9130(8) Å. The crossover temperature, at which T–O and M–O distances become equal (i.e., 1.927 Å), is found to be at 650 °C and corresponds to an inversion parameter x = 0.208(3). With increasing heat treatment, Raman spectra of quenched samples become significantly broadened and a peak characteristic for Mg, Al disorder at 721 cm−1 firstly appears for a crystal quenched from 800 °C with x = 0.248(4). At room temperature, photoluminescence spectra are dominated by a strong R line at 684.5 nm accompanied by poorly resolved N lines: N1 (687 nm), N2 (688 nm), and N3 (689 nm). N lines are caused by different Mg, Al environments of Cr3+. With increasing inversion parameter (x), the R line decreases in intensity and the N lines become prominent leading to strongly broadened peaks with a maximum shifted toward higher wave lengths (687.5 nm at 1,100 °C). Criteria for the detection of heat treatment on gemstone spinel applicable to gemological routine examination are provided. Extrapolation of u, a, and bond lengths from heat-treated Burma spinel toward the natural crystal suggests a retrograde “closing temperature” of ca. 400 ± 100 °C at which Mg, Al disorder was frozen.
Similar content being viewed by others
References
Andreozzi GB, Princivalle F (2002) Kinetics of cation ordering in synthetic MgAl2O4 spinel. Am Mineral 87:838–844
Andreozzi GB, Princivalle F, Skogby H, Della Giusta A (2000) Cation ordering and structural variations with temperature in MgAl2O4 spinel: an X-ray single crystal study. Am Mineral 85:1164–1171
Armbruster T, Bürgi HB, Kunz M, Gnos E, Brönnimann S, Lienert C (1990) Variation of displacement parameters in structure refinements of low albite. Am Mineral 75:135–140
Barpanda P, Behera SK, Gupta PK, Pratihar SK, Bhattacharya S (2006) Chemically induced disorder order transition in magnesium aluminium spinel. J Eur Ceram Soc 26(13):2603–2609
Basso R, Carbonin S, Della Giusta A (1991) Cation and vacancy distribution in a synthetic defect spinel. Z Krist 194:111–119
Burns RG (1993) Mineralogical applications of crystal field theory, 2nd edition. Cambridge University Press, UK 551 p
Cynn H, Sharma SK, Cooney TF, Nicol M (1992) High-temperature Raman investigation of order-disorder behavior in the MgAl2O4 spinel. Phys Rev B45:500–502
D’Ippolito V (2013) Linking crystal chemistry and physical properties of natural and synthetic spinels: an UV–VIS–NIR and Raman study. PhD Thesis, Sapienza Università di Roma, p 237
Della Giusta A, Princivalle F, Carbonin S (1986) Crystal chemistry of a suite of natural Cr-bearing spinels with 0.15 ≤ Cr ≤ 1.07. Neues Jajrb Miner Abh 155:319–330
Derkosch J, Mikenda W (1983) N-lines in the luminescence spectra of Cr3+-doped spinels: (IV) excitation spectra. J Lumines 28:431–441
Hadjiev VG, Iliev MN, Vergilov IV (1988) The Raman spectra of Co3O4. J Phys C: Solid State Phys 21:L199–L201
Hålenius U, Andreozzi GB, Skogby H (2010) Structural relaxation around Cr3+ and the red-green color change in the spinel (sensu stricto)-magnesiochromite (MgAl2O4–MgCr2O4) and gahnite-zincochromite (ZnAl2O4–ZnCr2O4) solid-solution series. Am Mineral 95:456–462
Hoang LC, Khoi NT, Quang VX, Minh NV, Jaing CC (2001) Some optical properties of Vietnam natural spinel. Proc. internat. workshop on material characterization by solid state spectroscopy: gems and minerals of Vietnam, Hanoi, 200–209
Hovestreydt E (1983) On the atomic scattering factor for O2−. Acta Crystallogr A39:268–269
Kunz M, Armbruster T (1990) Difference displacement parameters in alkali feldspars: effects of (Si, Al) order-disorder. Am Mineral 75:141–149
Lazzeri M, Thibaudeau P (2006) Ab initio Raman spectrum of the normal and disordered MgAl2O4 spinel. Phys Rev B74: 140301,1-140301,4
Lenaz D, Lughi V (2013) Raman study of MgCr2O4–Fe2+Cr2O4 and MgCr2O4–MgFe2 3+O4 synthetic series: the effects of Fe2+ and Fe3+ on Raman shifts. Phys Chem Minerals 40:491–498
Lenaz D, Skogby H, Princivalle F, Hålenius U (2004) Structural changes and valence states in the MgCr2O4–FeCr2O4 solid solution series. Phys Chem Minerals 31:633–642
Lucchesi S, Della Giusta A (1997) Crystal chemistry of a highly disordered Mg–Al natural spinel. Mineral Petrol 59:91–99
Maekawa H, Kato S, Kawamura K, Yokokawa T (1997) Cation mixing in natural MgAl2O4 spinel: a high temperature 27Al NMR study. Am Mineral 82:1125–1132
Malsy A-K, Klemm L (2010) Distinction of gem spinels from the Himalayan Montain Belt. Chimia 64:741–746
Malsy A-K, Karampelas S, Schwarz D, Klemm L, Armbruster T, Tuan DA (2012) Orange–red to orange–pink gem spinels from a new deposit at Lang Chap (Tan Huong-Truc Lau). Vietnam. J Gemmol 33:19–27
Méducin F, Redfern SAT (2004) Study of cation order-disorder in spinel by in situ neutron diffraction up to 1600 K and 3.2 GPa. Am Mineral 89:981–986
Mikenda W (1981) N-lines in the luminescence spectra of Cr3+-doped spinels: (III) partial spectra. J Lumines 26:85–98
Mikenda W, Preisinger A (1981a) N-lines in the luminescence spectra of Cr3+-doped spinels: (I) identification of N-lines. J Lumines 26:53–66
Mikenda W, Preisinger A (1981b) N-lines in the luminescence spectra of Cr3+-doped spinels: (II) origins of N-lines. J Lumines 26:67–83
Minh NV, Yang I-S (2004) A Raman study of cation-disorder transition temperature of natural MgAl2O4 spinel. Vibr Spec 35:93–96
Nassau K (1984) Gemstone Enhancement. Butterworths, p 272
Peterson RC, Lager GA, Hitterman RL (1991) A time-of-flight powder diffraction study of MgAl2O4 at temperatures up to 1273 k. Am Mineral 76:1455–1458
Phan T-L, Yu S-C, Phan M-H, Han TPJ (2004) Photoluminescence properties Cr3+-doped MgAl2O4 natural spinel. J Korean Phys Soc 45:63–66
Prince E. (2010) International Tables for Crystallography, Vol C, Wiley, p 1000
Princivalle F, Martignago F, Dal Negro A (2006) Kinetics of cation ordering in natural Mg(Al, Cr3+)2O4 spinels. Am Mineral 91:313–318
Redfern SAT, Harrison RJ, O’Neill H, St C, Wood DRR (1999) Thermodynamics and kinetics of cation ordering in MgAl2O4 spinel up to 1600°C from in situ neutron diffraction. Am Mineral 84:299–310
Rossmanith E, Armbruster T (1995) The intensity of forbidden reflections of pyrope: umweganregung or symmetry reduction? Z Kristallogr 210:645–649
Saeseaw S, Wang W, Scarratt K, Emmett JL, Douthit TR (2009) Distinguishing heated spinels from unheated natural spinels and from synthetic spinels: a short review of on-going research. http://www.giathai.net/pdf/Heated_spinel_Identification_at_May_25_2009.pdf. Retrieved 07/01/2014
Schmetzer K, Haxel C, Amthauer G (1989) Colour of natural spinels, gahnospinels and gahnites. N Jajrb Miner Abh 160:159–180
Schmocker U, Waldner F (1976) The inversion parameter with respect to the space group of MgAl2O4 spinels. J Phys C9:235–237
Sheldrick GM (2008) A short history of SHELX. Acta Cryst A64:112–122
Slotznick SP, Shim S-H (2008) In situ Raman spectroscopy measurements of MgAl2O4 spinel up to 1400°C. Am Mineral 93:470–476
Strek W, Derén P, Jezowska-Trzebiatowska B (1988) Optical properties of Cr3+ in MgAl2O4 spinel. Physica B152:379–384
Van Gorkom GGP, Haanstra JH, v d Boom JH (1973) Infrared and Raman spectra of the spinel ZnGa2O4. J Raman Spec 1:513–519
Wood DL, Imbusch GF, Macfarlane RM, Kisliuk P, Larkin DM (1968) Optical spectrum of Cr3+ ions in spinels. J Chem Phys 48:5255–5263
Yamanaka T, Takéuchi Y (1983) Order-disorder transition in MgAl2O4 spinel at high temperatures up to 1700°C. Z Kristallogr 165:65–78
Yui T-F, Zaw K, Wu C-M (2008) A preliminary stable isotope study on Mogok ruby Myanmar. Ore Geol Rev 24:192–199
Acknowledgments
We are highly indebted to Mariko Nagashima (Yamaguchi University, Japan) for performing the electron microprobe analyses. We are grateful to Rosa Micaela Danisi (Bern), Martin Fisch (Bern), and Veronica D’Ippolito (Rome, Italy) for revising a preliminary version of this manuscript. Reviews by Francesco Princivalle (Trieste, Italy) and an anonymous referee are highly appreciated.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Widmer, R., Malsy, AK. & Armbruster, T. Effects of heat treatment on red gemstone spinel: single-crystal X-ray, Raman, and photoluminescence study. Phys Chem Minerals 42, 251–260 (2015). https://doi.org/10.1007/s00269-014-0716-7
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00269-014-0716-7