Spectroscopy and X-ray structure refinement of sekaninaite from Dolni Bory (Czech Republic)

The crystal chemistry of sekaninaite from Dolni Bory, Czech Republic, was characterized by a multi-method approach. Particular emphasis was put on the characterization of the channel constituents (i.e. H2O and CO2). Electron microprobe analysis shows the sample to be close to the Fe endmember [X-Fe = Fe/(Fe+Mg) = 94%) with significant Mn (1.48 wt.%) present; laser ablation mass-spectrometry showed the presence of 0.42 wt.% Li2O. H2O and CO2 contents (1.48 and 0.17 wt.%, respectively) were determined via secondary-ion mass-spectrometry. Sample homogeneity was checked by Fourier-transform infrared (FTIR) imaging using a microscope equipped with a focal plane array detector. Single-crystal FTIR spectroscopy confirmed the presence of two types of H2O groups in different orientations (with prevalence of the type II orientation), and that CO2 is oriented preferentially normal to the crystallographic c axis. Using the Beer-Lambert relation, integrated molar coefficients, epsilon(i), were calculated for both types of H2O (epsilon(i) H2O[I] = 6000 +/- 2000; epsilon(i) H2O[II] = 13000 +/- 1000) and for CO2 (epsilon(i) CO2 = 2000 +/- 1000).