(Li, Na) Al (PO4) (F, OH)
Amblygonite [(Li, Na) Al (PO4) (F, OH)] is triclinic, and belongs to the space group Ci1 1. Corner-sharing [Alø5] chains (ø = unspecified ligand) extend parallel to the c-axis and are further linked along their length by PO4 tetrahedra to form type 1 [Al(PO4)ø3] chains. The tetrahedral vertices not linked to the central octahedral chain cross-link to adjacent chains to form a mixed tetrahedral-octahedral framework. The anion that bridges along the length of the [Alø5] octahedral chain is the OH or F anion, and the Li atom occupies a cavity surrounded by six anions in a distorted octahedral arrangement 2.
In the IR spectrum of amblygonite, the highest-frequency band at 3350 cm-1 is assigned to the OH stretching vibration. This band exhibits a characteristic behaviour, as its frequency and intensity decrease, and its broadness increases, when the fluorine percentage increases 3. Bands interpreted as being due to the stretching mode v3 of the PO43- ion are found at 1188, 1105 and 1025 cm-1. Similarly, the v2 vibrational mode of the phosphate ion produces bands at 485 and 420 cm-1 1. Some disagreements are present about bands observed at 630, 600 and 540 cm-1, as Farmer 1 believes that they are just due to the v4 bending mode of PO43-, while Fransolet et al. 3 argue that the AlO6 stretching vibrations also contribute to these bands. Furthermore, Farmer 1 argues that the band at 815 cm-1 should be assigned to AlO4 tetrahedra while Fransolet et al. 3 states that this frequency is due to the OH bending vibration. Other bands observed in the spectrum are found at 364 and 326 cm-1 3.
Raman spectrum of amblygonite contains bands at 3350, 1132, 1066, 1047, 1000, 915, 835, 642, 486, 424, and 307 cm-1approximately, with the bands at 1000 and 642 cm-1 being the strongest bands 4.
1. V.C. Farmer, 1974 Infrared spectra of minerals in Mineralogical Society Monograph 4 VC Farmer (Ed) pp 407-408, Mineralogical Society, London.
2. Groat, L. A., Raudsepp, M., Hawthorne, F. C., Ercit, T. S., Sherriff, B. L. and Hartman, J. S. (1990). The amblygonite-montebrasite series: Characterisation by single-crystal structure refinement, infrared spectroscopy , and multinuclear MAS-NMR spectroscopy, American Mineralogist, 75(9-10), 992-1008.
3. Fransolet, A. M. and Tarte, P. (1977). Infrared spectra of analysed samples of the amblygonite-montebrasite series: a new rapid semi-quantitative determination of fluorine, American Mineralogist, 62(5-6), 559-564.
4. Beny, C., Johan, V., Rossi, P. (1986). Discrimination et caracterisation de al herderite et de l'amblygonite / montebrasite dans le granite de Beauvoir (sondage GPF Echassieres) par microspectrometrie Raman, Principaux resultats scientifiques et techniques du BRGM, Paris, France, pp. 152-153.
SELECTED REFERENCES ON SPECTROSCOPY OF
AMBLYGONITE:
1. V.C. Farmer, 1974 Infrared spectra of minerals in Mineralogical Society Monograph 4 VC Farmer (Ed) pp 407-408, Mineralogical Society, London.
2. Fransolet, A. M. and Tarte, P. (1977). Infrared spectra of analysed samples of the amblygonite-montebrasite series: a new rapid semi-quantitative determination of fluorine, American Mineralogist, 62(5-6), 559-564.
3.
J.A. Gadsden 1975. Infrared spectra of minerals and related inorganic
compounds. Butterworths, London. Pp 141.
4. Beny, C., Johan, V., Rossi, P. (1986). Discrimination et caracterisation de al herderite et de l'amblygonite / montebrasite dans le granite de Beauvoir (sondage GPF Echassieres) par microspectrometrie Raman, Principaux resultats scientifiques et techniques du BRGM, Paris, France, pp. 152-153.
Original
spectra shown for this mineral can be obtained on request from J.T. Kloprogge
(E-mail t.kloprogge@qut.edu.au), or
R.L. Frost (E-mail r.frost@qut.edu.au).
Postal
address:
Centre
for Instrumental and Developmental Chemistry, Queensland University of
Technology, GPO Box 2434, Brisbane, Qld 4001, Australia.
Fax +61
7 3864 1804
For more information see our general website at: http://www.sci.qut.edu.au/sci_schps.html
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