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Members of the childrenite–eosphorite series, ideally (Fe 1-x Mn x) AlPO 4 (OH) 2⋅ H 2 O, from the highly evolved Homolka granite, in the southern Czech Republic, were characterized using a multi-analytical approach. They occur as anhedral grains, up to ∼0.2 mm in size, associated with quartz, muscovite, albite, and K-feldspar. Tiny inclusions of probable uraninite have been observed. Backscattered electron images reveal a patchy zoning of these members of the childrenite–eosphorite series, related to an uneven distribution of Fe and Mn. On the basis of electron microprobe analysis, the average composition of the studied material is (Fe 0.68 Mn 0.28 Ca 0.03)Σ0.99 Al 0.96 (P 1.04 Si 0.01)Σ1.05 O 4.00 (OH) 2.09⋅0.91 H 2 O, thus corresponding to childrenite. Unit-cell parameters of this species are a=6.9226(9) , b=10.4081(13) , c=13.3957(17) Å. Its crystal structure was refined in the space group Cmca down to R1=0.0295 on the basis of 602 unique reflections with Fo>4σ(Fo) and 66 refined parameters. The crystal structure analysis agrees with the results of electron microprobe analysis and suggests that, in the studied material, Fe occurs in the divalent oxidation state only. Crystal structure data are also consistent with the Raman spectrum collected on the same grain that was structurally characterized, confirming the occurrence of PO 4 groups only in childrenite. [ABSTRACT FROM AUTHOR]

Calcium oxalate phytoliths are one of the most prominent types of Ca speciation in the plant kingdom, and they store extensive amounts of carbon in crystalline form. Ca phytoliths were investigated in the root, trunk, and bark of Vitis vinifera Chasselas from a vineyard in Alsace, France. A multi-analytical approach was used, which included SEM coupled with EDX spectroscopy, XRD, XRF, TGA, and 13C-NMR spectroscopy. These techniques revealed that phytoliths are composed of crystalline calcium oxalate monohydrate (whewellite). The whewellite crystals exhibited mostly equant or short-prismatic habits in all of the three studied grapevine parts, but bipyramidal crystals also occurred. Raphide crystals were only observed in the root, where they were abundant. Instead of using wet chemical procedures to extract the mineral components from the organic parts of the biomass, a thermal treatment via calcination was chosen. The suitable temperature of calcination was determined through TGA experiments. The calcination of the biomass samples at 250 °C enhanced the amounts of Ca phytoliths in the residual chars. The thermal treatment, however, affected the appearance of the Ca oxalate crystals by producing surfaces that displayed macroporosity and by creating fractures. For calcination at both 300 °C and 350 °C, Ca oxalate lost a molecule of carbon monoxide to form Ca carbonate, and the modifications of the original crystal surfaces were more pronounced than those observed after thermal treatment at 250 °C. [ABSTRACT FROM AUTHOR]