Interpretation of the Metamorphic Processes in Various Rock Types Using the Chemistry of Garnets (Selecka Mountain, Macedonia)

The garnets from the complex of Selecka Mountain could be divided in two groups on the basis of their chemical composition and zoning. The garnets from muscovite-schist and amphibole-schist show characteristics typical for a growth in prograde metamorphic conditions up to the medium metamorphic grade. Characteristics of the other garnets (from aplite granite, aplite veins and metabasite) suggest their formation in anatectic or highly metasomatic conditions. The inversion in chemical zoning, observed in some of them, is discussed and related to possible processes of growth

Crystal structure of picotpaulite, TlFe2S3, from Allchar, FYR Macedonia

The crystal structure of the mineral picotpaulite, TlFe2S 3, was solved and refined using single-crystal X-ray diffraction data collected at room temperature. The symmetry is orthorhombic, space group Cmcm, with unit-cell parameters: a = 9.083(6), b = 10.754(6), c = 5.412(4) Å, V = 528.6(6) Å3, Z = 4. The structure was refined to the conventional R factor 0.0532 for 226 independent reflections with I > 2σ(I) and 21 variables. Picotpaulite is isostructural with minerals rasvumite (KFe2S3) and pautovite (CsFe2S 3), as well as with a number of synthetic compounds belonging to the CsCu2Cl3 structure type. The structure consists of double chains of FeS4-tetrahedra running along [001] interconnected by TlS10 coordination polyhedra, which form zig-zag chains along the same direction. The Fe-Fe distances between neighbours along the chain direction and perpendicular to it are 2.706(2) and 2.693(6) Å, respectively, indicating strong Fe-Fe interactions. The average oxidation state of Fe is +2.5, achieved by electron transfer over the close Fe sites. Thallium coordination polyhedron can be described as a combination of a square antiprism adjacent to a trigonal prism. The 6s2 electrons of Tl behave as an inert pair and the atom is situated in the centroid of its coordination

The Structure of Thorium(IV) Dititanium(IV) Oxide, ThTi206

The crystal structure of a modification of ThTbOG, obtained from the melt at 1100 °C, has been analysed by X-ray diffraction and refined to the R value of 0.051. The crystals are monoclinic with a= 1.0799(7), b = 0.8570(6), c = 0.5192(3) nm and p = 115.29(3)0 , space group C2/c, Z = 4, F(OOO) = 728. The structure is based on a near-hexagonal close-packing of the oxygen atoms, with the thorium and titanium atoms in »octahedral sites«. The coordination polyhedron of Th is a distorted square antiprism with Th-0 distances from 0.232 to 0.265 nm, that of Ti a distorted octahedron with Ti-0 distances from 0.187 to 0.201 nm like those characteristic for Ti02 polymorphs. The Ti coordination polyhedra form layers parallel_to the (100) which are connected by zig-zag chains of the Th coordination polyhedra which run in the [001] direction. The relations to another ThTi20 6 polymorph structure1 (isomorphous with brannerite) have been examined

Fumarolic Minerals: An Overview of Active European Volcanoes

The fumarolic mineralogy of the Icelandic active volcanoes, the Tyrrhenian volcanic belt (Italy) and the Aegean active arc (Greece) is investigated, and literature data surveyed in order to define the characteristics of the European fumarolic systems. They show broad diversity of mineral associations, with Vesuvius and Vulcano being also among the world localities richest in mineral species. Volcanic systems, which show recession over a longer period, show fumarolic development from the high-temperature alkaline halide/sulphate, calcic sulphate or sulphidic parageneses, synchronous with or immediately following the eruptions, through medium-temperature ammonium minerals, metal chlorides, or fluoride associations to the late low-temperature paragenesis dominated by sulphur, gypsum, alunogen, and other hydrous sulphates. The situation can be different in the systems that are not recessing but show fluctuations in activity, illustrated by the example of Vulcano where the high-temperature association appears intermittently. A full survey of the mineral groups and species is given in respect to their importance and appearance in fumarolic associations

Thermal stability of extended clusters in dravite. A combined EMP, SREF and FTIR study

A dravite from Yemen of near end-member composition was treated in air and hydrogen atmospheres at 600–900 °C to reveal changes in Mg and Al order over the octahedrally coordinated Y and Z sites, and to explore related changes in the characteristic vibrational bands in the principal (OH)-stretching frequency. Relevant infor- mation was obtained using electron microprobe analysis (EMPA), structural refinement (SREF) and polarized infra- red (IR) single-crystal spectroscopy. Overall, the EMPA, SREF and IR data show that only minor changes occur during thermal treatment up to at least 800 °C, including variations in structural parameters, Mg–Al order–disor- der and (OH)-stretching bands, indicating limited hydro- gen loss. Untreated and treated dravite samples have very similar long-range and short-range atomic structures, which may be related to the occurrence of stable Al–Mg extended clusters around the O1 (=W) and O3 (=V) sites: W(F)–Y(MgMgMg)–V(OH)3–Z[AlAlAlAlAl(Al,Mg)]; W(OH)–Y(MgMgAl)–V(OH)3–Z[AlAlAlAlAl(Al,Mg)]; W(O2–)–Y(AlAlAl)–V(OH)3–Z[AlAlAlAlAl(Al,Mg)]. These extended clusters remain stable to temperatures close

The crystal structure of balićžunićite, Bi2O(SO4)2, a new natural bismuth oxide sulphate

The crystal structure of balićžunićite, Bi2O(SO4)2, a new mineral species from "La Fossa" crater of Vulcano (Aeolian Islands, Italy), was solved from single-crystal X-ray-diffraction data and refined to R = 0.0507. The structure is triclinic, space group P-1, with lattice parameters a 6.7386(3), b 11.1844(5), c 14.1754(7) Å, α 80.082(2){degree sign}, β 88.462(2){degree sign}, γ 89.517(2){degree sign}, V 1052.01(8) Å3 and Z = 6. The crystal structure consists of 6 independent Bi sites, 6 S sites and 27 O sites of which 3 are oxo oxygen atoms not bonded to sulphur. Bi and S atoms are arranged close to an eutectic pattern parallel to the (100) crystal planes. The planes are stacked atom on atom such that Bi always overlays S and vice versa. This structural feature is shared with the known structure of the high temperature polymorph of the same compound, stable over 535oC. However, the sequences of Bi and S atoms in the two structures are different and so are the arrangements of oxygen atoms. Characteristic building blocks in the structure of balićžunićite are clusters of five Bi atoms which form nearly planar trapezoidal Bi5 groups with oxo oxygens located in the centres of the three Bi3 triangles which form the trapezoids. The trapezoidal Bi5O39+ ions are joined along [100] with SO42- groups by means of strong bismuth-sulphate oxygen bonds, forming infinite [100] rods with composition Bi5O3(SO4)51-. One sixths of Bi atoms do not participate in trapezoids, but form with additional SO42- groups rows of composition BiSO41+, also parallel to [100]. [Bi5O3(SO4)51-] rods form infinite layers parallel to the crystal plane (010) with [BiSO41+] rows located on the irregular surface of contact between adjacent layers. Bi atoms occur in four different coordination types, all showing the stereochemical influence of the Bi3+ lone electron pair. In this respect the crystal structure of balićžunićite shows greater variability than its high temperature polymorph which has only two types of Bi coordinations present in balićžunićite