Andrew J. Locock

An Excel spreadsheet to recast analyses of garnet into end-member components, and a synopsis of the crystal chemistry of natural silicate garnets

A Microsoft Excel spreadsheet has been programmed that allows users to calculate with ease the molar proportions of garnet end-members from chemical analyses. Recent advances in the understanding of the crystal chemistry of natural garnets, especially of the Ti-bearing garnets, are used to evaluate 29 end-members (15 species and 14 hypothetical end-members) for each analysis. The amounts of Fe^2^+ and Fe^3^+ (and Mn^3^+, if necessary) are calculated by stoichiometric constraints if these quantities have not been measured. The input data can include: SiO2, TiO2, ZrO2, SnO2, Y2O3, Al2O3, Sc2O3, Cr2O3, V2O3, FeO, Fe2O3, MnO, MgO, CaO, Na2O, H2O+ and F. The spreadsheet can be used with large data sets (up to 100 analyses at a time), and is accompanied by results calculated for 470 garnet analyses taken from the literature. The spreadsheet employs a simple scoring algorithm to measure the quality of a garnet analysis. The propagation of error from the input chemical data to the calculation of end-member proportions is also discussed briefly.

An Excel spreadsheet to classify chemical analyses of amphiboles following the IMA 2012 recommendations

A Microsoft Excel spreadsheet has been programmed to assist with classification of chemical analyses of orthorhombic and monoclinic amphiboles following the 2012 nomenclature recommended by the International Mineralogical Association. The spreadsheet is intended for use only with compositional data (wt% oxides and halogens, rather than atomic proportions) and provides options for the estimation of Fe3+/ΣFe and Mn3+/ΣMn ratios and OH content. Various cation normalization schemes can be automatically or manually selected. For each analysis, the output includes the group, subgroup (or B-occupancy for the oxo-amphiboles), and species name including any mandatory chemical prefixes, along with a formula based on 24 anions. The formula results can be exported in a form suitable for the AMPH2012 program. Prefixes related to space groups (proto-) and suffixes (-P21/m) are not assigned in the spreadsheet. Large data sets (up to 200 analyses at a time) can be accommodated by the spreadsheet, which is accompanied by results calculated for more than 650 amphibole analyses taken from the literature. .Display Omitted A spreadsheet to classify amphiboles using the IMA 2012 nomenclature is presented.Output includes group, subgroup, species name and formula.Up to 200 analyses can be classified.Results for more than 650 analyses are tabulated.

Spectroscopy of the cation distribution in the schorlomite species of garnet

Abstract A homogeneous megacryst of schorlomite was investigated to determine the valence states of Fe and Ti and the crystallographic sites occupied by these elements. The chemical composition of the specimen was analyzed by electron microprobe, wet-chemical analysis, FTlR, and INAA. The results from X-ray absorption near-edge structure spectroscopy (XANES) are consistent with exclusively Ti4+ occupying the octahedral site only. The tetrahedral site is deficient in Si and the results of low-temperature 57Fe Mossbauer spectroscopy indicate that the remainder of the site is occupied by Fe3+ and substantial Fe2+. A spin-allowed intensified crystal-field transition of [4]Fe2+ is present in the near-infrared spectrum. The optical absorption spectrum is dominated by an intense band centered at 500 nm with a full width of 8000 cm-1 at half maximum peak height; this band is assigned to an Fe2+-Ti4+ intervalence charge transfer transition between ,[4]Fe2+ and [6]Ti. The cation site occupancies in this specimen of schorlomite can be expressed by the following formula: {Ca2.866Mg0.800Na0.038Mn0.019}Σ3.003 [Ti4+1.058Fe3+0.631 Al0.137Fe2+0.057 Mg0.055Zr0.039V3+0.014Mn0.013] Σ2.004 - (Si2.348Fe3+0.339Fe2+0.311 [4H]0.005)Σ3.003O12.

Chapter 6 – Crystal chemistry of actinide phosphates and arsenates

Publisher Summary This chapter presents an overview of the crystal structures of inorganic compounds in which actinide polyhedra are directly coordinated by phosphate or arsenate tetrahedra. Arsenates are considered for comparative purposes, because of the very similar structural roles played by arsenate and phosphate ions. Structural data are taken mainly from the Inorganic Crystal Structure Database and the published literature. In natural settings, uranium phosphate species are among the most numerous, widespread, abundant and insoluble of actinide-bearing minerals and largely control the mobility of actinides in groundwater and in actinide contaminated soils and sediments. The structures and behavior of uranium-bearing and thorium-bearing phosphate minerals thus provide a basis from which to predict the long-term behavior of actinide-bearing phosphates. Data are tabulated for a given structure type, with phosphates separated from arsenates, and organized in order of increasing atomic number of the actinide present.

Evaluating the applicability of portable-XRF for the characterization of Hokkaido Obsidian sources: a comparison with INAA, ICP-MS and EPMA

AbstractnAs a result of the limited application of portable X-ray fluorescence (pXRF) in archaeological research in Japan it is necessary to compare this technique to proven, laboratory-based, analytical techniques. In this study instrumental neutron activation analysis, inductively-coupled plasma mass spectrometry, and electron probe microanalysis are used to validate pXRF and determine the overall suitability of this technique for archaeological obsidian provenance studies in Hokkaido, northern Japan. Furthermore, the results of this study are compared to previously published data to assess reproducibility and compatibility. This study demonstrates the reliability of pXRF for the rapid characterization of Hokkaido obsidian while contributing to the ongoing evaluation of the applicability of “off-the-shelf” pXRF to obsidian provenance research in archaeology.

Miniaturization of mechanical milling for powder X-ray diffraction

To enable mechanical milling of small (0.1–1.0xa0g) samples, a cylindrical grinding vessel machined from polypropylene and furnished with tungsten carbide rods has been designed and produced for use inside the conventional jar of a McCrone Micronizing Mill. The vessel is about one-seventh the volume of the conventional jar supplied by the manufacturer. The conditions of milling for both the conventional and the miniaturized-grinding assemblies were tested using quartz sand as a limiting case. The median grain sizes of the resultant powders were measured by an X-ray gravitational-sedimentation method, with contamination from the grinding media measured by Rietveld refinement and by instrumental neutron activation analysis. The use of tungsten carbide grinding elements permits rapid wet milling of a small sample to the same median grain size in about one-third of the time required by a regular sample ground in corundum. The relative contamination (by tungsten carbide on a weight basis) using the miniaturized-grinding assembly is about 6(1)% of the proportion of corundum contamination yielded by the conventional grinding assembly.

Geochronology, classification and mantle source characteristics of kimberlites and related rocks from the Rae Craton, Melville Peninsula, Nunavut, Canada

Detailed geochronology along with petrographic, mineralogical and geochemical studies have been conducted on recently found diamond-bearing kimberlitic and related rocks in the Rae Craton at Aviat and Qilalugaq, Melville Peninsula, north-east Canada. Magmatic rocks from the Aviat pipes have geochemical (both bulk rock and isotopic) and mineralogical signatures (e.g., core to rim Al and Ba enrichment in phlogopite) similar to Group I kimberlite. In contrast, Aviat intrusive sheets are similar to ‘micaceous’ Group II kimberlite (orangeite) in their geochemical and mineralogical characteristics (e.g., phlogopite and spinel compositions, highly enriched Sr isotopic signature). Qilalugaq rocks with the least crustal contamination have geochemical and mineralogical signatures [e.g., high SiO2, Al2O3 and H2O; low TiO2 and CO2; less fractionated REE (rare earth elements), presence of primary clinopyroxene, phlogopite and spinel compositions] that are similar to features displayed by olivine lamproites from Argyle, Ellendale and West Greenland. The Naujaat dykes, in the vicinity of Qilalugaq, are highly altered due to extensive silicification and carbonation. However, their bulk rock geochemical signature and phlogopite chemistry are similar to Group I kimberlite. U–Pb perovskite geochronology reveals that Aviat pipes and all rocks from Qilalugaq have an early Cambrian emplacement age (540–530xa0Ma), with the Aviat sheets being ~30xa0Ma younger. This volatile-rich potassic ultramafic magmatism probably formed by varying degrees of involvement of asthenospheric and lithospherically derived melts. The spectrum of ages and compositions are similar to equivalent magmatic rocks observed from the nearby north–eastern North America and Western Greenland. The ultimate trigger for this magmatism could be linked to Neoproterozoic continental rifting during the opening of the Iapetus Ocean and breakup of the Rodinia supercontinent.

Perovskite classification: An Excel spreadsheet to determine and depict end-member proportions for the perovskite- and vapnikite-subgroups of the perovskite supergroup

Abstract Perovskite mineral oxides commonly exhibit extensive solid-solution, and are therefore classified on the basis of the proportions of their ideal end-members. A uniform sequence of calculation of the end-members is required if comparisons are to be made between different sets of analytical data. A Microsoft Excel spreadsheet has been programmed to assist with the classification and depiction of the minerals of the perovskite- and vapnikite-subgroups following the 2017 nomenclature of the perovskite supergroup recommended by the International Mineralogical Association (IMA). Compositional data for up to 36 elements are input into the spreadsheet as oxides in weight percent. For each analysis, the output includes the formula, the normalized proportions of 15 end-members, and the percentage of cations which cannot be assigned to those end-members. The data are automatically plotted onto the ternary and quaternary diagrams recommended by the IMA for depiction of perovskite compositions. Up to 200 analyses can be entered into the spreadsheet, which is accompanied by data calculated for 140 perovskite compositions compiled from the literature.

Building an Outdoor Classroom for Field Geology: The Geoscience Garden.

ABSTRACT Many geoscience educators have noted the difficulty that students experience in transferring their classroom knowledge to the field environment. The Geoscience Garden, on the University of Alberta North Campus, provides a simulated field environment in which Earth Science students can develop field observation skills, interpret features of Earths crust in three dimensions, and discover Earth history. The garden consists of large (1–5 m) boulders and rock slabs arranged in a landscaped layout that represents the geology of western and northern Canada. The project adds a unique capability for teaching basic field skills to students in a local environment and prepares them for field courses at more remote locations. Students work in the garden in a second-year introductory structural geology class that precedes a field school. Student perceptions of the effectiveness of the installation were evaluated using surveys of students returning from field school. Initial responses were positive; students returning from field school after the introduction of the garden reported significantly greater satisfaction with their ability to collect field data.