Search

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 Earth's 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.

Estimates of the oxidation states of magmas are important to current investigations of the geochemical characteristics of their source regions and of evolved magmatic series created during differentiation. One means of achieving such estimates is to capitalize on compositions of coexisting cubic and rhombohedral Fe-Ti oxides determined by electron microprobe. A combination of experimental calibration points and thermodynamic modeling provides a basis for translating such compositions into T-ƒO2 values. This has been done until recently by estimating Fe3+/ΣFe on the basis of charge balance and stoichiometry by the method of Droop (1987), after matrix corrections of X-ray intensity data have been performed, as EPMA cannot be used routinely to distinguish different elemental valence states, much less accurately quantify abundances of Fe3+ and Fe2+. The traditional approach of undertaking post-data-reduction calculations falls short of attaining the best possible quantitative results. The tactical choice of not accounting for light elements that have not been explicitly analyzed prior to matrix corrections of X-ray intensity data leads to systematic errors in reported oxide abundances for measured elements. This article addresses one such issue, the oxygen associated with Fe3+ (hereafter "excess oxygen"), on the basis of coexisting Fe-Ti oxides from Andean lavas. A new software routine in probe for EPMA (PFE) uses an iterative calculation scheme to calculate amounts of excess oxygen that would not be considered if all iron were assumed to be ferrous and then applies this excess oxygen during matrix corrections. The PFE approach reveals that Fe-concentrations have been underestimated, universally, in these minerals because O atoms absorb FeKα radiation: discrepancies increase as total Fe and Fe3+/Fe2+, hence excess oxygen, increase. Analyses of the most Fe-rich cubic oxide compositions in this data set have ~6 wt% excess oxygen and ~1 wt% more FeO+Fe2O3 than would be reported without incorporating the impact of excess oxygen in matrix corrections. Minor to negligible differences in other elements are also observed. These effects are not because excess oxygen is directly attributed to these elements, although some may be present in multiple valence states, as matrix corrections are undertaken on the basis of the conventional assumptions that they occur as Cr3+, V3+, Mn2+, Mg2+, Ca2+, and Si4+. Rather, variably small increases in total Fe propagate through the matrix corrections for other elements, and these differences may be recorded as minor increases or decreases in some concentrations, depending on the particular element and the amount of change in Fe-concentration. Fe3+/ΣFe in analyses produced with the PFE routine are essentially identical to those determined in the traditional mode, as cation proportions calculated on the basis of charge balance and stoichiometry, with the method of Droop (1987), is a necessary step. The new method: (1) provides more accurate concentrations, mainly for Fe and Ti; (2) is applicable to any mineral containing ferric iron (subject to stoichiometric constraints); (3) provides more accurate analytical totals, which can be advantageous for evaluating analytical quality; and (4) does not impact estimates of oxidation state. Oxygen fugacities and temperatures determined with the model of Ghiorso and Evans (2008) are essentially unchanged. [ABSTRACT FROM AUTHOR]

Heamanite-(Ce) (IMA 2020-001), ideally (K0.5Ce0.5)TiO3, is a new perovskite-group mineral found as an inclusion in a diamond from the Gahcho Kué mine in the Northwest Territories, Canada. It occurs as brown, translucent single crystals with an average maximum dimension of ~80 μm, associated with rutile and calcite. The luster is adamantine, and the fracture conchoidal. Heamanite-(Ce) is the K-analog of loparite-(Ce), ideally (NaCe)Ti2O6. The Mohs hardness is estimated to be 5½ by comparison to loparite-(Ce), and the calculated density is 4.73(1) g/cm3. Electron microprobe wavelength-dispersive spectrometric analysis (average of 34 points) yielded: CaO 10.70, K2O 7.38, Na2O 0.16, Ce2O3 13.77, La2O3 8.22, Pr2O3 0.84, Nd2O3 1.59, SrO 6.69, BaO 2.96, ThO2 0.36, PbO 0.15, TiO2 45.77, Cr2O3 0.32, Al2O3 0.10, Fe2O3 0.09, Nb2O5 0.87, UO3 0.01, total 99.98 wt%. The empirical formula, based on 3 O atoms, is: [(K0.268Na0.009)Σ0.277(Ce0.143La0.086Pr0.009Nd0.016)Σ0.254(Ca0.326Sr0.110Ba0.033Pb0.001)Σ0.470Th0.002]Σ1.003 (Ti0.979Nb0.011Cr0.007Al0.003Fe0.002)Σ1.002O3. The Goldschmidt tolerance factor for this formula is 1.003. Heamanite-(Ce) is cubic, space group Pm3m, with unit-cell parameter a = 3.9129(9) Å, and volume V = 59.91(4) Å3 (Z = 1). The crystal structure was solved using single-crystal X‑ray diffraction data and refined to R1(F) = 2.61%. Heamanite-(Ce) has the aristotypic perovskite structure and adopts the same structure as isolueshite and tausonite. The six strongest diffraction lines are [dobs in angstroms (I in percentages) (hkl)]: 2.764 (100) (110), 1.954 (41) (200), 1.596 (36) (211), 1.045 (16) (321), 1.236 (13) (310), and 1.382 (10) (220). The Raman spectrum of heamanite-(Ce) shows two broad bands at 560 and 787 cm−1, with no bands observed above 1000 cm−1. Heamanite-(Ce) is named after Larry Heaman, a renowned scientist in the field of radiometric dating applied to diamond-bearing kimberlites, mantle-derived eclogites, and lamprophyre dikes. The dominant REE should appear as a Levinson suffix, hence heamanite-(Ce). [ABSTRACT FROM AUTHOR]

The crystal structures of synthetic hallimondite and synthetic parsonsite have been refined by full-matrix least-squares techniques to agreement indices (hallimondite, parsonsite) w[R.sub.2], of 5.5, and 7.6% for all data, and R1 of 2.7 and 3.4%, calculated for 339l and 3181 unique observed reflections (|[F.sub.0]| [greater than or equal to] 4[[sigma].sub.F]), respectively. Hallimondite is triclinic, space group P[bar.1], Z = 2, a = 7.1153(8), b = 10.4780(12), c = 6.8571(8) A, [alpha] = 101.178(3)[degrees], [beta] = 95.711 (3)[degrees], [gamma] = 86.651 (3)[degrees], V = 498.64(3) [A.sup.3], and is isostructural with parsonsite, triclinic, space group P[bar.1], Z = 2, a = 6.8432(5), b = 10.4105(7), c = 6.6718(4) A, [alpha] = 101.418(1)[degrees], [beta] = 98.347(2)[degrees], [gamma] = 86.264(2)[degrees], V = 460.64(5) [A.sup.3]. In both structures, hexavalent uranium occurs as a uranyl pentagonal bipyramid. The uranyl polyhedra share an edge, forming dimers that are linked by edge- and vertex-sharing with arsenate or phosphate tetrahedra to form chains along [001]. Two symmetrically distinct Pb positions connect the chains. In hallimondite, a partially occupied oxygen atom is located in the cavity between the uranyl arsenate chains and Pb positions, and is attributed to an [H.sub.2]O group. The crystal of synthetic parsonsite investigated does not have appreciable electron density at this position, but its structural cavity is large enough to contain [H.sub.2]O. The presence of [H.sub.2]O in synthetic hallimondite, and its absence in synthetic parsonsite, are supported by the results of FTIR spectroscopy. In conjunction with thermogravimetric results from the literature, we suggest that the formula of parsonsite should be considered [Pb.sub.2][(U[O.sub.2])[(P[O.sub.4).sub.2]][([H.sub.2]O).sub.n], and hallimondite, [Pb.sub.2][(U[O.sub.2])[(As[O.sub.4).sub.2]][([H.sub.2]O).sub.n], with 0 [less than or equal to] n [less than or equal to] 0.5 in each case.

Autunite, Ca[[(U[O.sub.2])(P[O.sub.4]).sub.2]][([H.sub.2]O).sub.11], is amongst the most abundant and widely distributed of the uranyl phosphate minerals, yet because of its pseudo-tetragonal symmetry and rapid dehydration in air, the details of its symmetry, stoichiometry, and structure were previously uncertain. The crystal structure of synthetic autunite was solved by direct methods and refined by full-matrix least-squares techniques to agreement indices [R.sub.1] = 0.041, calculated for the 1497 unique observed reflections (|[F.sub.o]| [greater than or equal to] 4[[sigma].sub.F]), and w[R.sub.2] = 0.119 for all data. Autunite is orthorhombic, space group Pnma, Z = 4, a = 14.0135(6), b = 20.7121(8), c = 6.9959(3) [Angstrom], V = 2030.55(15) [[Angstrom].sup.3]. The structure contains the well-known autunite type sheet with composition [[(U[O.sub.2])(P[O.sub.4])].sup.-], resulting from the sharing of equatorial vertices of the uranyl square bipyramids with the phosphate tetrahedra. The calcium atom in the interlayer is coordinated by seven [H.sub.2]O groups and two longer distances to uranyl apical O atoms. Two symmetrically independent [H.sub.2]O groups are held in the structure only by hydrogen bonding. Bond-length-constrained refinement provided a crystal-chemically reasonable description of the hydrogen bonding.

Nixonite (IMA 2018-133), ideally Na2Ti6O13, is a new mineral found within a heavily metasomatized pyroxenite xenolith from the Darby kimberlite field, beneath the west-central Rae Craton, Canada. It occurs as microcrystalline aggregates, 15 to 40 mm in length. Nixonite is isostructural with jeppeite, K2Ti6O13, with a structure consisting of edge- and corner-shared titanium-centered octahedra that enclose alkali-metal ions. The Mohs hardness is estimated to be between 5 and 6 by comparison to jeppeite, and the calculated density is 3.51(1) g/cm3. Electron microprobe wavelength-dispersive spectroscopic analysis (average of 6 points) yielded: Na2O 6.87, K2O 5.67, CaO 0.57, TiO2 84.99, V2O3 0.31, Cr2O3 0.04, MnO 0.01, Fe2O3 0.26, SrO 0.07, total 98.79 wt%. The empirical formula, based on 13 O atoms, is: (Na1.24K0.67Ca0.06)S1.97(Ti5.96V0.023Fe0.018)S6.00O13 with minor amounts of Cr and Mn. Nixonite is monoclinic, space group C2/m, with unit-cell parameters a = 15.3632(26) Å, b = 3.7782(7) Å, c = 9.1266(15) Å, b = 99.35(15)°, and V = 522.72(1) Å3, Z = 2. Based on the average of seven integrated multi-grain diffraction images, the strongest diffraction lines are [dobs in Å (I in %) (hkl)]: 3.02 (100) (310), 3.66 (75) (110), 7.57 (73) (200), 6.31 (68) (201), 2.96 (63) (311), 2.96 (63) (203), and 2.71 (62) (402). The five main Raman peaks of nixonite, in order of decreasing intensity, are at 863, 280, 664, 135, and 113 cm–1. Nixonite is named after Peter H. Nixon, a renowned scientist in the field of kimberlites and mantle xenoliths. Nixonite occurs within a pyroxenite xenolith in a kimberlite, in association with rutile, priderite, perovskite, freudenbergite, and ilmenite. This complex Na-K-Ti-rich metasomatic mineral assemblage may have been produced by a fractionated Na-rich kimberlitic melt that infiltrated a mantle-derived garnet pyroxenite and reacted with rutile during kimberlite crystallization. [ABSTRACT FROM AUTHOR]

Goldschmidtite is a new perovskite-group mineral (IMA No. 2018-034) with the ideal formula (K,REE,Sr)(Nb,Cr)O3. A single grain of goldschmidtite with a maximum dimension of ∼100 μm was found as an inclusion in a diamond from the Koffiefontein pipe in South Africa. In addition to the dark green and opaque goldschmidtite, the diamond contained a Cr-rich augite (websteritic paragenesis) and an intergrowth of chromite, Mg-silicate, and unidentified K-Sr-REE-Nb-oxide. Geothermobarometry of the augite indicates that the depth of formation was ∼170 km. The chemical composition of gold-schmidtite determined by electron microprobe analysis (n = 11, WDS, wt%) is: Nb2O5 44.82, TiO2 0.44, ThO2 0.10, Al2O3 0.35, Cr2O3 7.07, La2O3 11.85, Ce2O3 6.18, Fe2O3 1.96, MgO 0.70, CaO 0.04, SrO 6.67, BaO 6.82, K2O 11.53, total 98.53. The empirical formula (expressed to two decimal places) is (K0.50La0.15Sr0.13Ba0.09Ce0.08)Σ0.95(Nb0.70Cr0.19Fe0.05Al0.01Mg0.04Ti0.01)Σ1.00O3. Goldschmidtite is cubic, space group Pm3m, with unit-cell parameters: a = 3.9876(1) Å, V = 63.404(6) Å3, Z = 1, resulting in a calculated density of 5.32(3) g/cm3. Goldschmidtite is the K-analog of isolueshite, (Na,La)NbO3. Raman spectra of goldschmidtite exhibit many second-order broad bands at 100 to 700 cm–1 as well as a pronounced peak at 815 cm–1, which is possibly a result of local ordering of Nb and Cr at the B site. The name goldschmidtite is in honor of the eminent geochemist Victor Moritz Goldschmidt (1888–1947), who formalized perovskite crystal chemistry and identified KNbO3 as a perovskite-structured compound. [ABSTRACT FROM AUTHOR]

The new uranyl phosphate [(UO2)3(PO4)(OH)(H2O)2](H2O) with an unprecedented structure is synthesized at 150 and 185 degrees Celsius. The structure contains uranyl phosphate chains composed of uranyl pentagonal and hexagonal bipyramids and phosphate tetrahedra linked by sharing of polyhedra edges.

The uranyl mineral swamboite has been redefined to swamboite-(Nd) and its structure has been solved and refined as a commensurate structure in sixdimensional superspace. The structure is monoclinic, superspace group P21/m(a1, b1, g1)00(-a1, b1, g1)00 (a2,0,g2)0s, cell parameters a = 6.6560(3), b = 6.9881(5), c = 8.8059(6), c = 11.3361(16) Å, ß = 102.591(5)°, modulation wave-vectors q1 = 1/3 1/3 0; q2 = -1/3 1/3 0; q3 = 1/2 0 1/2. The structure was refined from 8717 reflections to a final R = 0.0610. The model includes modulation both of atomic positions and displacement parameters, as well as occupancy waves. The structure is based upon uranyl-silicate sheets of uranophane topology alternating with an interlayer of partly occupied Nd3+ sites and H2O molecules. The strong (3 + 3) dimensional modulation of the structure originates from the distribution of the Nd-dominated sites and further accommodation of the suitable geometry within the sheets and charge distribution within the structure. The separation distances between the corresponding occupied Nd sites are rationals of the super-cell vectors corresponding to the modulation vectors of the structure. The case of swamboite-(Nd) is the first example of a modulated structure within the oxysalts of U6+. [ABSTRACT FROM AUTHOR]

The garnet supergroup includes all minerals isostructural with garnet regardless of what elements occupy the four atomic sites, i.e., the supergroup includes several chemical classes. There are presently 32 approved species, with an additional 5 possible species needing further study to be approved. The general formula for the garnet supergroup minerals is {X3}[Y2](Z3)φ12, where X, Y, and Z refer to dodecahedral, octahedral, and tetrahedral sites, respectively, and φ is O, OH, or F. Most garnets are cubic, space group ... (no. 230), but two OH-bearing species (henritermierite and holtstamite) have tetragonal symmetry, space group, I41/acd (no. 142), and their X, Z, and φ sites are split into more symmetrically unique atomic positions. Total charge at the Z site and symmetry are criteria for distinguishing groups, whereas the dominant-constituent and dominant-valency rules are critical in identifying species. Twenty-nine species belong to one of five groups: the tetragonal henritermierite group and the isometric bitikleite, schorlomite, garnet, and berzeliite groups with a total charge at Z of 8 (silicate), 9 (oxide), 10 (silicate), 12 (silicate), and 15 (vanadate, arsenate), respectively. Three species are single representatives of potential groups in which Z is vacant or occupied by monovalent (halide, hydroxide) or divalent cations (oxide). We recommend that suffixes (other than Levinson modifiers) not be used in naming minerals in the garnet supergroup. Existing names with suffixes have been replaced with new root names where necessary: bitikleite-(SnAl) to bitikleite, bitikleite-(SnFe) to dzhuluite, bitikleite-(ZrFe) to usturite, and elbrusite-(Zr) to elbrusite. The name hibschite has been discredited in favor of grossular as Si is the dominant cation at the Z site. Twenty-one end-members have been reported as subordinate components in minerals of the garnet supergroup of which six have been reported in amounts up to 20 mol% or more, and, thus, there is potential for more species to be discovered in the garnet supergroup. The nomenclature outlined in this report has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (Voting Proposal 11-D). [ABSTRACT FROM AUTHOR]

The article presents information on new minerals. One of the minerals investigated was found at the Byrud emerald mine in Norway. A description of the fluoro-magnesiohastingsite mineral is given, and the origin of the georgbarsanovite mineral is discussed. Other minerals mentioned in the article include Manganiandrosite-Cerium and Vanadoandrosite-Cerium.

The article focuses on the minerals from the Pine Point deposits in the Northwest Territories. The Pine Point district first attracted economic attention because of the prospectors on their way to the Klondike gold rush more than a century ago. The deposit yielded numerous types of minerals, including zinc and rock salt.

The crystal structures of synthetic hallimondite and synthetic parsonsite have been refined by full-matrix least-squares techniques to agreement indices (hallimondite, parsonsite) wR2 of 5.5, and 7.6% for all data, and R1 of 2.7 and 3.4%, calculated for 3391 and 3181 unique observed reflections (¦Fo¦ ≥ 4σF), respectively. Hallimondite is triclinic, space group P1, Z = 2, a = 7.1153(8), b = 10.4780(12), c = 6.8571(8) Å, α = 101.178(3)°, β = 95.711(3)°, γ = 86.651 (3)°, V = 498.64(3) ų, and is isostructural with parsonsite, triclinic, space group P1, Z = 2, a = 6.8432(5), b = 10.4105(7), c = 6.6718(4) Å, α = 101.418(1)°, β = 98-347(2)°, γ = 86.264(2)°, V = 460.64(5) ų. In both structures, hexavalent uranium occurs as a uranyl pentagonal bipyramid. The uranyl polyhedra share an edge, forming dimers that are linked by edge- and vertex-sharing with arsenate or phosphate tetrahedra to form chains along [001]. Two symmetrically distinct Pb positions connect the chains. In hallimondite, a partially occupied oxygen atom is located in the cavity between the uranyl arsenate chains and Pb positions, and is attributed to an H2O group. The crystal of synthetic parsonsite investigated does not have appreciable electron density at this position, but its structural cavity is large enough to contain H2O. The presence of H2O in synthetic hallimondite, and its absence in synthetic parsonsite, are supported by the results of FTIR spectroscopy. In conjunction with thermogravimetric results from the literature, we suggest that the formula of parsonsite should be considered Pb2[(UO2)(PO4)2](H2O)n, and hallimondite, Pb2[(UO2)(AsO4)2](H2O)n with 0 ≤ n ≤ 0.5 in each case. [ABSTRACT FROM AUTHOR]