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The crystal-chemistry of okanoganite-(Y): an example of (sims+empa+sref) multi-analytical approach to solve a complex problem.
No full textThe crystal structure of piergorite-(Ce), Ca8Ce2(Al0.5 Fe3+0.5) Σ 1(□,Li,Be)2Si6B8O36(OH,F)2: A new borosilicate from Vetralla, Italy, with a modified hellandite-type chain
No full textPiergorite-(Ce) is a new mineral found at Tre Croci, Vetralla, Italy with simplified formula Ca8Ce2 (Al0.5Fe0.53+)∑1(□,Li,Be)2Si6B8O36(OH,F)2. It occurs as strong intergrowths of small crystals, colorless to pale yellow, associated with sanidine, mica, magnetite, rutile, titanite, and other Th-U-REE bearing minerals, in miarolitic cavities of a syenitic ejectum. Piergorite-(Ce) is biaxial negative, nα = 1.717 (1), nβ = 1.728 (1), and nγ = 1.735 (1), 2Vmeas = 68(2)°, X = b, and Z ^ c = 7(1)°. Crystals show tabular habit and a very good {010} cleavage; twinning along the (30-1) plane produces “L” forms. The three strongest lines in the simulated powder diffraction pattern (dobs, I, hkl) are: 2.65 Å, 100.0, (213, -413); 1.91 Å, 48.3, (223, -423, 821); 2.90 Å, 44.9, (-603, -612). The structure was solved by Patterson synthesis from X-ray diffraction data [monoclinic, space group P2/a, a = 28.097(3) Å, b = 4.777(1) Å, c = 10.236(2) Å, β = 96.81(1)°, V = 1364.2(7) Å3, Z = 2] and was refined to a final Robs = 0.059 for 6480 Fo with Io > 3σ (Io). The structure shows similarities with the hellandite group because Si and B tetrahedra form chains along c. Hellandite structure is characterized by a single chain of five-membered rings, whereas piergorite-(Ce) shows a double chain of five-membered rings interconnected by a single octahedral site to form a three-dimensional framework containing five independent eightfold-coordinated M sites and a partly occupied T-cavity
The crystal chemistry of piergorite, (Ca8REE2)10 (Al0.5Fe0.5) (vac, Li,Be)2Si6B8O36(OH,F)2: a new REE-borosilicate from Tre Croci, Vetralla, Italy.
No full textWater, lithium and trace element compositions of olivine from Lanzo South replacive mantle dunites (Western Alps): New constraints into melt migration processes at cold thermal regimes
Get PDFNew perspectives on the origin of olivine-rich troctolites and associated harrisites from the Ligurian ophiolites (Italy)
No full textDetails of the analytical techniqu
Ti-rich garnets: an EPMA, SIMS, Mossbauer, XRPD and SCXRD investigations
Get PDFA suite of Ti-bearing garnets from magmatic, metamorphic and carbonatitic rocks was studied by Electron Probe Microanalysis (EPMA), X-ray Powder Diffraction (XRPD), Single Crystal X-ray Diffraction (SCXRD), Mössbauer spectroscopy and Secondary Ion Mass Spectrometry (SIMS) in order to better characterize their crystal chemistry. The studied garnets show TiO2 varying in the ranges 4.9(1)-17.1(2) wt.% and variable Fe3+/ΣFe content. SIMS analyses allowed quantification of light elements yielding H2O in the range 0.091(7)-0.46(4), F in the range 0.004(1)-0.040(4) and Li2O in the range 0.0038(2)-0.014(2) wt%. Mössbauer analysis provided spectra with different complexity, which could be fitted to a number of components variable from one (YFe3+) to four (YFe2+, ZFe2+, YFe3+, ZFe3+). A good correlation was found between the Fe3+/ΣFe resulting from the Mössbauer analysis and that derived from the Flank method (Höfer & Brey, 2007).
X-ray powder analysis revealed that the studied samples are a mixture of different garnet phases with very close cubic unit cell parameters as recently found by other authors (Antao, 2013). Single crystal X-ray refinements using anisotropic displacement parameters were performed in the Ia-3d space group and converged to R1 in the range 1.63-2.06 % and wR2 in the range 1.44-2.21 %. Unit cell parameters vary between 12.0641(1) and 12.1447(1) Å, reflecting different Ti contents and extent of substitutions at tetrahedral site.
The main substitution mechanisms affecting the studied garnets are: YR4+ + ZR3+
↔ ZSi + YR3+ (schorlomite substitution); YR2+ + ZR4+
↔ 2YR3+ (morimotoite substitution); YFe3+↔ YR3+ (andradite substitution) with ZR4+ = Ti;
YR4+ = Ti, Zr; YR3+ = Fe3+, Al3+, Cr3+; ZR3+ = Fe3+, Al3+ and YR2+ = Fe2+, Mg2+, Mn2+. The 2YTi4++ ZFe2+ ↔ 2YFe3+ +
ZSi4+, the hydrogarnet substitution [(SiO4)4-↔ (O4H4)4-], the F– ↔ OH– and the YR4+ + XR+ ↔ YR3+ + XCa2+, with YR4+ =
Ti, Zr; YR3+ = Fe3+, Al3+, Cr3+; XR+ = Na, Li also occur.
The garnet crystal chemistry and implications in terms of nomenclature and classification (Grew et al., 2013) are discussed.
Antao S.M. 2013. The mystery of birefringent garnet: is the symmetry lower than cubic?. Powder diffr., 28(4), 281-287.
Grew E.S., Locock A.J., Mills S.J., Galuskina I.O., Galuskina E.V. & Hålenius U. 2013. Nomenclature of the Garnet Supergroup. Am. Mineral., 98, 785-811.
Höfer H.E. & Brey G.P. 2007. The iron oxidation state of garnet by electron microprobe: Its determination with the flank method combined with major-element analysis. Am. Mineral., 92, 873-885
The crystal structure of peprossiite-(Ce), an anhydrous REE, and Al mica-like borate with square-pyramidal coordination for Al.
No full textCrystal chemistry and light elements analysis of Ti-rich garnets
Get PDFA suite of Ti-bearing garnets from magmatic, carbonatitic, and metamorphic rocks was studied by
electron probe microanalysis (EPMA), X-ray powder diffraction (XRPD), single-crystal X-ray diffraction (SCXRD), Mössbauer spectroscopy, and secondary ion mass spectrometry (SIMS) to better
characterize their crystal chemistry. The studied garnets show TiO2 varying in the range of 4.9(1) to
17.1(2) wt% and variable Fe3+/ΣFe content. SIMS analyses allowed quantification of light elements
yielding H2O in the range 0.091(7)–0.46(4), F in the range 0.004(1)–0.040(4), and Li2O in the range
0.0038(2)–0.014(2) wt%. Mössbauer analysis provided spectra with different complexity, which could
be fitted to several components variable from one (YFe3+) to four (YFe2+, ZFe2+, YFe3+, ZFe3+). A good
correlation was found between the Fe3+/ΣFe resulting from the Mössbauer analysis and that derived
from the Flank method.
X-ray powder analysis revealed that the studied samples are a mixture of different garnet phases with
very close cubic unit-cell parameters as recently found by other authors. Single-crystal X-ray refinement
using anisotropic displacement parameters were performed in the Ia3d space group and converged to
1.65 ≤ R1 ≤ 2.09% and 2.35 ≤ wR2 ≤ 3.02%. Unit-cell parameters vary in the range 12.0641(1) ≤ a ≤
12.1447(1) Å, reflecting different Ti contents and extent of substitutions at tetrahedral site.
The main substitution mechanisms affecting the studied garnets are: YR4+ + ZR3+ ↔ ZSi + YR3+
(schorlomite substitution); YR2+ + ZR4+ ↔ 2YR3+ (morimotoite substitution); YR3+ ↔ YFe3+ (andradite
substitution); in the above substitutions YR2+ = Fe2+, Mg2+, Mn2+; ZR4+ = Ti; YR3+ = Fe3+, Al3+, Cr3+; ZR3+ = Fe3+, Al3+. Minor substitutions, such as 2YTi4++ ZFe2+ ↔ 2YFe3+ + ZSi, (SiO4)4– ↔ (O4H4)4–, F–
↔
OH–
, and YR4+ + XR+ ↔ YR3+ + XCa2+, with YR4+ = Ti, Zr; YR3+ = Fe3+, Al, Cr3+; XR+ = Na, Li also occu
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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