Dark blue lazurite from the Malo-Bystrinskoe lazurite deposit, Baikal Lake area, Eastern Siberian region, Russia, was analyzed by electron microprobe and revealed an unusually high content of total sulfur corresponding to 8.3 wt% S. The relative content of sulfur in sulfate and sulfur in sulfide form was determined by wet chemical analysis. The H2O content was measured by means of differential thermal analysis in combination with mass spectrometry and infrared (IR) spectroscopy. The charge-balanced empirical formula of lazurite calculated on the basis of 12 (Al+Si) atoms per formula unit was (Na6.97Ca0.88K0.10)Σ7.96[(Al5.96Si6.04)Σ12O24](SO4)1.092−(S3−)0.55S0.052− Cl0.04·0.72H2O. The presence of H2O molecules and (S3)– and (SO4)2– groups was confirmed by the combination of IR, Raman, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) methods. The idealized formula of lazurite is Na7Ca[Al6Si6O24](SO4)2–(S3)–·H2O, and it is believed that extra-framework cations and anions are grouped into clusters of [Na3Ca·SO4]3+ and [Na4(S3)–]3+. The types of isomorphous substitutions in nosean and haüyne are discussed. Lazurite is a clathrate-type mineral, which may be an effective (S3)– sensor due to the stability of the trisulfur radical anion in isolated cages of the crystal structure. This specific feature makes it possible to study the behavior of this ubiquitous radical anion over larger T and P ranges as compared to free species. This kind of lazurite, with oxidized and reduced sulfur species, seems to be appropriate for the estimation of the fugacity of SO2 and O2 in metasomatic systems forming lazurite-containing rocks. The systematic presence of incommensurate modulations is a unique structural feature of Baikal lazurite and may be an important marker indicating provenance of the mineral.

Trace element (TE) partitioning in the system "mineral-hydrothermal solution" is studied by the method of thermo-gradient crystal growth coupled with internal sampling of a fluid phase. The analytical procedure used enables evaluating of structurally bound and superficially bound modes of TE in crystals and determining corresponding dual partition coefficients. The case of precious metals (PM-Au, Pt, Pd) at 450 and 500 • C and 100 MPa pressure is considered. The minerals are pyrite, As-pyrite, magnetite, Mn-magnetite and hematite and fluids are ammonium chloride-based hydrothermal solutions. The partition coefficients for structural and surficial modes, D str p and D sur p , are found to be unexpectedly high (except for Au in pyrite). High concentrations of PM are attributed to superficial nonautonomous phases (NAPs), which can be considered as primary concentrators of PM. We also have studied the co-crystallization (exchange) coefficients (D e) of REE (Ce, Eu, Er, Yb) and Fe in magnetite and hematite at 450 • C and 100 MPa. D sur e is elevated to two orders of magnitude as compared to D str e. It is shown that not only physicochemical parameters affect REE distribution in hydrothermal systems, but also NAP presence and its composition. The crystal growth mechanism specified by the agency of NAP is suggested. The study of PM distribution in natural pyrite of gold-ore deposits supported the importance of differentiating between structurally and superficially bound TE modes for correct use of experimental D values to determining element concentrations in ore-forming fluids.

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The interfacial crystal layer of poorly soluble mineral grown under hydrothermal conditions is modified chemically into a surficial nonautonomous phase (SNAP) and, in this capacity, takes part in growth process, doing several important functions. This paper considers some of them related to geochemistry and mineralogy. The new interpretation is given to the following phenomena: (1) selection of components during crystal growth in multiphase associations; (2) stability of multiphase parageneses having a common chemical component; (3) dual character of the distribution coefficients due to different properties of the crystal volume and SNAP; (4) formation of nano- and microinclusions of unusual composition different from the basic mineral phase; (5) spatial ordering of nano- and microparticles during their directed aggregation at the growing crystal face; (6) accumulation of valuable components (primarily noble metals), incompatible in most of mineral matrixes, in the surficial layer; and (7) effect of “hidden” metal content, associated with the presence of noble metals in the SNAP or of nano- and microinclusions formed during the SNAP evolution.

The isomorphism of S-bearing feldspathoids belonging to the cancrinite, sodalite, tugtupite, vladimirivanovite, bystrite, marinellite and scapolite structure types has been investigated using a multimethodical approach based on infrared, Raman and electron spin resonance (ESR), as well as ultraviolet, visible and near infrared (UV–Vis–near IR) absorption spectroscopy methods and involving chemical and X-ray diffraction data. Sapozhnikovite Na8(Al6Si6O24)(HS)2 and sulfite and thiosulfate analogues of cancrinite are synthesized hydrothermally and characterized by means of electron microprobe analyses, powder X-ray diffraction and Raman spectroscopy. The possibility of the incorporation of significant amounts of SO42−, S4 and SO32− in the crystal structures of cancrisilite, sulfhydrylbystrite and marinellite, respectively, has been established for the first time. Thermal conversions of S-bearing groups in the synthetic sulfite cancrinite and sapozhnikovite analogues as well as natural vladinirivanovite and S4-bearing haüyne under oxidizing and reducing conditions have been studied using the multimethodical approach. The SO42− and S2− anions and the S3·– radical anion are the most stable S-bearing species under high-temperature conditions (in the range of 700–800 °C); their ratio in the heated samples is determined by the redox conditions and charge-balance requirement. The HS− and S52− anions are stable only under highly reducing conditions.