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X-ray diffraction Rietveld structure refinement and mid- and far-infrared spectral studies have been done on Ga-for-Al and Ge-for-Si substituted synthetic clintonites (Cln), CaMg 2 (Al 4-x Ga x )(Si 1-y Ge y ) O 10 (OH,OD) 2  (x = 0.0-4.0, y = 0.0-1.0). Rietveld analyses indicate that there is complete solid-solution in both the (Al 4-x Ga x )Si-, (Al 4-x Ga x )Ge-clintonite series. With increasing Ga-for-Al, the mean tetrahedral bond-length, &lt;T-O&gt;, and mean tetrahedral basal oxygen separation, &lt; [4] O bas -O bas &gt; increase, whereas the octahedral and interlayer parameters, the tetrahedral rotation angles (α), and the dimensional misfits (D) vary little. With increasing Ga-for-Al substitution in the Si-series the broad OH and OD stretching bands shift downward from 3607 to 3529 cm -1  and from 2671 to 2620 cm -1 , respectively. For the Ge-series samples, the OH and OD stretching bands shift downward from 3610 to 3523 cm -1  and from 2667 to 2611 cm -1 , respectively. According to the data of the curve fitting analysis, both the OH and OD-stretching bands are modeled by at least three broad [wider than 37 cm -1  of full-width at half height (FWHH)] I bands (M1M2M2 = MgMgAl 3+ /MgMgGa 3+ ) and a narrow (FWHH = 23-33 cm -1 ) and weak N band (M1M2M2 = MgMgMg) on the highest frequency side. In some samples, a very weak and broad V (one vacant M site) band at the lowest frequency region is observed. Tetrahedral Si-O, Al-O, and Ga-O stretching bands lie in fairly discrete regions, which are at 1030-830, 880-760, and 790-640 cm -1 , respectively. However, the band regions for both the tetrahedral Al-O and Ge-O stretching as well as the Ge-O and Ga-O stretching bands closely overlap each other. In the 720-500 cm -1  region, Si-O-Al, Al-O-Al, Si-O-Ga, Al-O-Ge, Al-O-Ga, Ge-O-Ga, and Ga-O-Ga deformational bands (tetrahedral-chain bending and “breathing” modes) are observed to overlap strongly. Around 300 and 200 cm -1  one observes the Ca-O inner  and Ca-O outer  stretching bands, respectively, which show a slight downward frequency shift (-7 cm -1  per Ga apfu) with Ga-for-Al substitution.

american mineralogist

Mid- and far-infrared spectra of synthetic CaMg 2 (Al 4–x Ga x )(Si 1–y Gey)O 10 (OH,OD) 2 - clintonite: Characterization and assignment of the Ca-O inner  and Ca-O outer  stretching bands