• journal_title：American Mineralogist
• Contributor：Frank C. Hawthorne ; Mark D. Welch ; Giancarlo Della Ventura ; Shuangxi Liu ; Jean-Louis Robert ; David M. Jenkins
• Publisher：Mineralogical Society of America
• Date：2000-
• Format：text/html
• Language：en
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：85
• issue：11-12
• firstpage：1716
• section：Articles

Fourier-transform infrared spectra (FTIR) were recorded on a series of synthetic amphiboles along the join Ca_1.8Mg_5.2Si₈O₂₂(OH)₂–Ca_1.8(Mg_4.2Al)(Si₇Al)O₂₂(OH)₂. The spectra were fitted by up to six component bands by optimization and non-linear least-squares techniques. ²⁷Al MAS NMR and triple-quantum (3Q) MAS NMR spectra were recorded for the synthetic amphibole Ca_1.8(Mg_4.8Al_0.4)(Si_7.6Al_0.4)O₂₂(OH)₂. The fitted FTIR and NMR spectra show that ^VIAl occurs at the M2 site and at the M1 or M3 sites; by analogy with previous crystal-structure refinement results on natural amphiboles, ^VIAl occupancy of M2 and M3 is presumed. The fine structure present in the FTIR spectra indicates that they are also affected by NNN (next-nearest-neighbor) interactions. There are two types of NNN arrangements: (1) SiSi or SiAl at adjacent T1T1 dimers; (2) permutation of Mg/Al over M2M2M3 sites. Discounting those arrangements unlikely on bond-valence grounds, there are two arrangements that give rise to five distinct bands in the infrared spectra. There are two principal conclusions: (1) infrared spectra of amphiboles in the principal OH-stretching region can be affected significantly by NNN effects; (2) the small number of bands due to NNN effects indicates that amphiboles show strong short-range order.