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1.  Cu- and Mn-bearing tourmalines from Brazil and Mozambique: crystal structures, chemistry and correlations 
Mineralogy and Petrology  2012;107:265-279.
Cu- and Mn-bearing tourmalines from Brazil and Mozambique were characterised chemically (EMPA and LA-ICP-MS) and by X-ray single-crystal structure refinement. All these samples are rich in Al, Li and F (fluor-elbaite) and contain significant amounts of CuO (up to ~1.8 wt%) and MnO (up to ~3.5 wt%). Structurally investigated samples show a pronounced positive correlation between the distances and the (Li + Mn2+ + Cu + Fe2+) content (apfu) at this site with R2 = 0.90. An excellent negative correlation exists between the distances and the Al2O3 content (R2 = 0.94). The samples at each locality generally show a strong negative correlation between the X-site vacancies and the (MnO + FeO) content. The Mn content in these tourmalines depends on the availability of Mn, on the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO and CuO we believe that the Cu content in tourmaline is essentially dependent on the availability of Cu and on stereochemical constraints.
PMCID: PMC4811101  PMID: 27069308
2.  Ba2Gd2(Si4O13): a silicate with finite Si4O13 chains 
Ba2Gd2(Si4O13) contains finite Si4O13 chains and Gd2O12 dimers. It is a representative of a rare class of silicates containing Si4O13 chains.
The title compound, dibarium digadolinium(III) tetra­silicate, crystallized from a molybdate-based flux. It represents a new structure type and contains finite zigzag-shaped C 2-symmetric Si4O13 chains and Gd2O12 dimers built of edge-sharing GdO7 polyhedra. The [9+1]-coordinated Ba atoms are located in voids in the atomic arrangement. All atoms are in general positions except for one O atom, which lies on a twofold axis. The structure is compared with those of the few other known tetra­silicates.
PMCID: PMC2855576  PMID: 20203391

Results 1-2 (2)