Orthorhombic lazurite from the Tultui deposit in the Baikal region

Abstract

A lazurite sample taken from the Tultui deposits in the Baikal region has been studied using pet rographic examination, X ray diffraction, and local X ray spectroscopy (electron microprobe). It is estab lished that the line of the basic cell in the X ray diffraction pattern of the orthorhombic lazurite is widened, so the unit cell parameters should be recalculated from the interlayer distances of the superstructural reflec tions. The chemical compositions and unit cell parameters of the lazurites from the Baikal region and the Pamirs are different. Two schemes of the chemical substitutions of atoms in the mineral are assumed: (1) the hauyne cluster [Na 3 CaSO 4 ] 3+ is replaced with a sodalite cluster [Na 4 Cl] 3+ , and (2) two hauyne clusters 2[Na 3 CaSO 4 ] 3+ are substituted by nosean clusters [Na 4 SO 4 ] + and [Na 4 H 2 O] 4+ with retention of the total charge. The increase in the Na and Cl contents in the orthorhombic lazurite is accompanied by a decrease in the unit cell dimensions. Orthorhombic lazurites from the southern Baikal region and the southwestern Pam irs were formed in apocarbonate (apocalciphyre) metasomatic rocks at a lower temperature than pyroxene, afghanite, and cubic lazurite.

Anion-Centered Tetrahedra in Inorganic Compounds

“…The cristobalite-like topology is well-recognized for the framework of anion-centered tetrahedra that occur in the structure of Hg–Sb pyrochlore, [Hg 2 O]­[Sb 2 O 6 ] (Figure ). Weil reported synthesis and structure of [Hg 2 O]­(SeO 3 )­(H 2 O) 0.167 , an amazing compound, which, under the inspection from the viewpoint of O-centered tetrahedra, appears to be an inverted analogue of cancrinite, a common aluminosilicate framework mineral , (Figure ). Another interesting compound of the same sort is [Hg 2 N]­(NO 3 ), which again possess the [NHg 2 ] + framework, but with rather complicated topology consisting of three- and four-membered rings (Figure ).…”

Structure Modulations and Symmetry of Lazurite-Related Sodalite-Group Minerals

“…The unit cells of the corresponding reciprocal lattices are highlighted in gray in Figure 2a,c. Later, the composition, structure, and properties of triclinic and orthorhombic LRMs were reinvestigated in [10] and [8,17], respectively. Specific features that made it possible to approve both crystals as new mineral species were revealed.…”

“…At that time, this mineral did not yet have its own name and was considered to be an orthorhombic variety of lazurite. Later, this orthorhombic LRM was characterized using various methods [8,17], including powder diffraction on samples from the Tultui gem lazurite deposit situated in the southwestern Baikal region. The orthorhombic symmetry served as the basis for identifying these crystals as a new mineral species called vladimirivanovite [8].…”