STUDIUM OPTICKÝCH ANOMÁLIÍ V GRANÁTECH Z CA-SKARNŮ BRNĚNSKÉHO, ŠUMPERSKÉHO A ŽULOVSKÉHO MASIVU

Optical anisotropy commonly occurs in grossular-andradite garnets from different types of Ca-skarns. The difference between the crystal chemistry of isotropic and non-isotropic lamellae is discussed. It is assumed that the substitution of OH groups and fluorine for oxygen or entire SiO4 tetrahedra is the main cause of the occurrence of optical anomalies in the studied samples, rather than Fe3+/Al3+ordering on the positions of trivalent cations, as some previous authors suggest

Xenotime dissolution dynamics under neutral and acidic conditions

Dissolution dynamics of synthesized xenotime was experimentally studied in a discontinuous flow–through reactor. The dissolution rate constants derived from yttrium release were determined as (1.71 ± 0.74) × 10-17 mol/m2/s in near neutral solution (pH = 5.4) and (3.77 ± 0.91) × 10-15 mol/m2/s in strongly acidic solution (pH = 1.14). Compared to the dissolution dynamics of other minerals, xenotime (1) has better stability than, e.g., quartz or even monazite under given conditions and (2) could be potentially considered as suitable collector for fixation of the radionuclides from radioactive waste.Dissolution dynamics of synthesized xenotime was experimentally studied in a discontinuous flow–through reactor. The dissolution rate constants derived from yttrium release were determined as (1.71 ± 0.74) × 10-17 mol/m2/s in near neutral solution (pH = 5.4) and (3.77 ± 0.91) × 10-15 mol/m2/s in strongly acidic solution (pH = 1.14). Compared to the dissolution dynamics of other minerals, xenotime (1) has better stability than, e.g., quartz or even monazite under given conditions and (2) could be potentially considered as suitable collector for fixation of the radionuclides from radioactive waste

The Gel Growth Technique—A Neglected Yet Effective Tool to Prepare Crystals of Oxysalts and Supergene Minerals

The technique of crystal growth in gels has nowadays become somewhat neglected in the scope of earth sciences, to the disadvantage of the experimental mineralogist. Even preparing an inorganic silica gel can prove a challenge to many, let alone successfully configure the entire experiment. Based not only on previous literature but also on our extensive experience, crystals of many substances, including supergene minerals as reference standards, can be successfully grown in gel, aiding in accomplishing various research goals in earth sciences. Instead of providing the reader with an overwhelming compendium of historical information and theoretical knowledge of the subject which can be found elsewhere, we presented herein a comprehensive, practically oriented guide to the understanding and successful use of the technique of crystal growth in gels, mentioning, in addition to the general principle, the numerous pitfalls which we encountered during our own use of the method, and the ways to overcome them. Despite that the procedure is nowadays used mainly for the laboratory synthesis of organic or metal-organic compounds, we believe it to be a valuable asset to any mineralogist, and often, the only way to obtain inorganic reference material of a particular mineral of interest

Photoluminescence of synthetic titanite-group pigments: A rare quenching effect

Chromium-doped titanite and malayaite samples, which were synthesised to evaluate their performance as ceramic pigments, show remarkable photoluminescence behaviour. Emissions of centres related to traces of trivalent rare-earth elements (REE) are observed exclusively from chromium-free samples. Their Cr-doped analogues (containing the same REEs on the same concentration levels), in contrast, only show broad-band Cr3+ emission whereas all REE emissions are suppressed. This behaviour is assigned to quenching of REE emissions by chromium centres (i.e., REE3+ → Cr3+ energy transfer)

Contributions to the stereochemistry of zirconium oxysalts—part III: syntheses and crystal structures of M2+Zr(SO4)3 with M = Mg, Mn, Co, Ni, Zn and Cd, and a note on (Fe3+,2+,Zr)2(SO4)3 and Fe2(SO4)3

The novel compounds M2+Zr(SO4)3 with M = Mg, Mn, Co, Ni, Zn, and Cd as well as (Fe3+,2+,Zr)2(SO4)3 were synthesized at mild hydrothermal conditions (Teflon-lined stainless steel vessels, 220 °C) from the mixtures of Zr2O2(CO3)(OH)2, the respective M2+(SO4)·nH2O hydrated salts, H2SO4 and a minor amount of water. Crystals up to several tenths of a mm in size were obtained within a few days and studied at 200 K by single-crystal X-ray diffraction techniques. All these compounds belong to the structure type of monoclinic Fe2(SO4)3; they are either isotypic in space group P21/n (No. 14), Z = 4, i.e. M2+Zr(SO4)3 with M = Mn, Co, Ni, Zn, and Cd as well as the mixed valence sulfate (Fe3+,2+,Zr)2(SO4)3 or in the case of MgZr(SO4)3, closely related but with a larger unit cell, in space group Pc and Z = 8. The framework of the monoclinic Fe2(SO4)3 structure is characterized by two types of isolated Fe3+O6 octahedra, corner-linked with three types of sulfate groups. In the isotypic M2+Zr(SO4)3 series, the Fe3+ atom on the Fe(1) position is substituted by Zr4+ while M2+ ions occupy the Fe(2) site in the ferric sulfate structure type. Mean cation-oxygen bond lengths (S[4]: 1.462–1.472 Å; Zr[6]: 2.053–2.060 Å as well as M2+–O distances) are generally rather short, but still within the range reported in literature.© The Author(s) 201