Electronic absorption spectra of chromium-bearing amesite
Platonov, Alexej N.; Langer, Klaus; Wieviöra, Andrzej; Andrut, Michael
European Journal of Mineralogy Volume 7 Number 4 (1995), p. 961 - 966
published: Aug 1, 1995
manuscript accepted: Feb 22, 1995
manuscript received: Jul 15, 1994
ArtNo. ESP147050704021, Price: 29.00 €
Abstract The crystal field parameters of Cr3+-ions in amesite (Mg2Al)[SiAlO5(OH)4], calculated from polarized optical absorption spectra (Dq = 1782cm-1, B = 694cm-1, ß = 0.756, CFSE = 61.2 kcal mol-1) are close to those of Cr3+-ions in Cr-clinochlore (kämmererite). This can be explained by the similarities of the arrangement of the Al- and Mg-octahedra in the aluminum-bearing octahedral layers of both mineral structures. The high Dq value of Cr3+-ions, incorporated in relatively large octahedral positions (Rcr-o = 2.03 Å in amesite and 1.97 Å in clinochlore) obviously result from the considerable influence of the next-nearest cations (Mg2+) on the effective charge of the ligands in the Cr3+-centred octahedral sites.