The degree of metamictization in zircon: a Raman spectroscopic study
Nasdala, Lutz; Irmer, Gert; Wolf, Dieter
European Journal of Mineralogy Volume 7 Number 3 (1995), p. 471 - 478
published: May 19, 1995
manuscript accepted: Jan 17, 1995
manuscript received: Sep 1, 1994
ArtNo. ESP147050703001, Price: 29.00 €
Abstract A series of natural zircon samples representing various degrees of metamictization were investigated by Raman microprobe (RMP) analysis. We found systematic changes in wavenumbers and half-widths of the Raman bands, caused by increasing irregularities of bond-lengths and bond-angles and a general breaking-up of the structure as a result of metamictization. Therefore, Raman spectroscopy can be used to measure the crystallinity of zircons. The half-width of the antisymmetric stretching vibration band (Big) of the SiO4 tetrahedra, which has a frequency of about 1007 cm-1 in well-crystallized and 1000 to 955 cm-1 in metamict zircons, is most suitable for estimating the degree of metamictization: Its value increases from about 5 cm-1 in well crystallized samples up to 30-55 cm-1 in highly metamict, X-ray-amorphous zircons, and is strongly dependent on the degree of lattice destruction by metamictization. In contrast, the Raman parameters seem to be almost uninfluenced by chemical variations. The potential value and advantages of such RMP measurements, especially in radiometric age determinations, are discussed in the light of other methods.