Diss.--Åbo, 1756. / At head of title: J.H.W.N. Reproduction of original from Kress Library of Business and Economics, Harvard University. Goldsmiths'-Kress no. 09103.1-1A. Includes bibliographical references.

No description available.

The crystal-chemistry and paragenesis of astrophyllite group minerals (AGM) from over- and undersaturated alkaline rocks has been documented by a combination of electron microprobe analyses, single-crystal and powder X-ray diffraction, Mossbauer spectroscopy, Fourier-transform infrared spectroscopy, nuclear reaction analysis, thermal gravitational analysis, thermal decomposition, wet-chemical methods and optical measurements. A standardized general formula for AGM has been developed, based on 31 anions, and is of the form A2BC7D 2T8O26(OH)4X 0-1, where [10]--[13]A = K, Rb, Cs, H3O+, H2O, or □; [10] B = Na or Ca; [6]C = Mn, Fe2+ Fe3+ Na, Mg, or Zn; D = [6]Ti, Nb, or Zr; [4]T = Si or Al and X = &phis; = F, OH, O, or □. Results from Mossbauer spectroscopy, bond valence sums and thermodynamic calculations indicate F to order at X [&phis;(16)] whereas the monovalent anion sites in the O-sheet are host solely to OH- . On this basis, eight species and two AGM polytypes are recognized, the most recent, niobokupletskite, identified from Mont Saint-Hilaire during the course of this study. The AGM heterophyllosilicate structure consists of two composite sheets stacked along [001] in a 2:1 ratio resulting in a layered HOH structure. Single-crystal X-ray refinements indicate the existence of two kupletskite polytypes, kupletskite-1A and kupletskite-Ma2b2c, the result of polytypic stacking of identical HOH layers. Mossbauer spectroscopy indicates all Fe to be present in the O-sheet, and Fe3+/Fe tot ratios in AGM to range from 0.01 to 0.21, corresponding to 0.05 to 0.56 apfu Fe3+, confirming that Fe 2+ is the dominant valence state for iron in the AGM structure. AGM from oversaturated alkaline intrusions are characterized by a restricted range of Mn/Mn+Fetot (0.03 to 0.69) and enrichments in K, Rb, Ti (with positive values of Nb-Zr) and Si. AGM from undersaturated intrusions display a wide range in Mn/Mn+Fetot, (0.09 to 1.00) and have been further subdivided into a kupletskite subgroup (Mn/Mn+Fetot ≥ 0.50) and an astrophyllite subgroup (Mn/Mn+Fetot < 0.50). Kupletskite subgroup samples are enriched in Na, Mn, Zn, Fe3+, Nb and Zr (with positive values of Nb-Zr), whereas astrophyllite subgroup samples are enriched in K, Ca, Fe2+, Ti, Zr (with negative values of Nb-Zr) and F. Crystal-chemical parameters in AGM (such as Mn/Mn+Fetot and Nb/Nb+Zr) can be used as petrogenetic indicators. At Mont Saint-Hilaire (Quebec), two distinct paragenetic trends are recognized in the AGM population: (1) an oxidizing magmatic to post-magmatic oxidizing trend resulting in enrichment of the AGM in Na, Mn, Fe3+ and Nb, and (2) a reducing trend resulting in enrichment in Ca, Fe2+, Zr and F by hydrothermal or metasomatic processes. The second evolutionary trend is thought to be the result of interaction of an exsolved magmatic fluid with either meteoric waters or sediments. Both trends lend evidence for late-stage mobilization and concentration of high field-strength elements (such as Nb and Zr) in highly alkaline systems.

[No abstract available] / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

[No abstract available] / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Orapa A/K-1 kimberlite pipe occurs within a cluster of more than thirty pipes in east-central Botswana and is noted for preserving a nearly complete stratigraphic section of the original diatreme. Deep-seated nodules from the Orapa pipe include (1) an oxide suite comprised of ilmenite, rutile, and ilmenite-rutile intergrowths, (2) a silicate suite comprised of garnet, clinopyroxene, and various silicate-oxide intergrowths, and (3) a lithic suite comprised primarily of ecologites and various crustal rocks. The compositions of individual ilmenite nodules are typical of those in kimberlites with MgO values varying between 7 and 15 wt. % and Cr(,2)O(,3) contents averaging approximately 2.5 wt. %. Marked peripheral zoning in magnesium content is probably indicative of reaction with the transporting kimberlitic magma. Discrete nodules of rutile and rutile host containing ilmenite lamellae recovered from this pipe are first reported in the literature and are characterized by rutile with up to 13.5 wt. % Nb(,2)O(,5) and 8 wt. % Cr(,2)O(,3). Results from experiments involving controlled conditions of temeperature and oxygen fugacity (1 atm) suggest the importance of TI('3+)-bearing chromian armalcolite as a possible high pressure precursor to the ilmenite-rutile intergrowths. The clinopyroxene and garnet discrete nodules are diopsidic and pyropic, respectively, in composition. Large differences in corresponding Cr(,2)O(,3) contents indicate that these discrete nodules did not originate by disaggregation of the associated eclogites. The eclogites from Orapa include foliated and non-foliated textural types and have been reported to contain both diamond and graphite. Compositions of the garnet and clinopyroxene coexisting in these eclogites suggest temperatures of equilibration consistent with upper mantle conditions when plotted on model geotherms determined for neighboring areas in southern Africa. The petrographic and mineral chemical data presented in this study demonstrate an overall close similarity between the Orapa nodule suite and those representative of other, more thoroughly investigated districts in Africa, Siberia, and the United States. The Orapa suite is distinctive, however, in its wide variety of oxide discrete nodules, the presence of certain complex silicate/oxide intergrowths, and the previously reported coexistence of diamond and graphite in eclogite.

No description available.

No description available.

Abstract not available

No description available.