Gabrielle E. Hamburger

Bio: Gabrielle E. Hamburger is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Tourmaline. The author has an hindex of 1, co-authored 1 publications receiving 21 citations.

A "Simplexity Principle" and Its Relation to "Ease" of Crystallization

Abstract: Crystallization is viewed as a kinetic process, the relative "ease" of which is influenced by details of the structures involved The word "simplexity" is used as a measure of structural complexity In general, high "simplexity" is synonymous with disorder, or structural simplicity, or high entropy Nucleation and growth of phases with high simplexity are favored-in many cases over more stable compounds of lower simplexity The aluminosilicate minerals are examined from this point of view Available information on laboratory syntheses is used as some measure of "ease" of crystallization The crystal-chemical similarity of $Al^{3+}$ and $Si^{4+}$ and the fact that they may play either equivalent or nonequivalent roles in different structures are related to the development of preferred phases Those compounds with both Al and Si in equivalent 4-co-ordinated positions (high simplexity) are readily synthesized The compounds with Al and Si in ordered 4-co-ordinated positions or those ordered by virtue of havi

Coupled substitutions in the tourmaline group

Abstract: Statistical analysis of 136 natural tourmaline compositions from the literature reveals the presence and extent of coupled substitutions involving several cations and structural sites. In schorls and dravites these are a dehydroxylation type substitution (1) (OH)−+R2+ = R3++O2− and an alkali-defect type substitution (2) R++R2+ = R3++□, Al3+ being the predominant R3+ action. Substitution (1) which represents solid solution towards a proton-deficient end-member, R+ R 3 3+ R 6 3+ (BO3)3 Si6O18O3(OH), accounts for three times as much of the observed compositional variability as does (2) which represents substitution toward a hypothetical alkali-free end-member, □(R 2 2+ R3+) R 6 3+ (BO3)3Si6O18(OH)4. The occurrence of both of these substituions produces intermediates between end-member schorl/ dravite, R+ R 3 2+ R 6 3+ (BO3)3Si6O18(OH)4, and a new series within the tourmaline group, R 1−x + R 3 3+ R 6 3+ (BO3)3Si6O18O3−x (OH)1+x. In addition to dehydroxylation type, 2(OH)−+Li+ = R3++202−, and possibly alkali-defect type, 2R++Li+ = R3++2□, substitutions, a third type Li++O2− = (OH)−+□, occurs in the elbaites giving rise to Li-poor, proton-rich species. All three substitutions serve to reduce the Li-content of natural elbaite which, as a result, does not attain the composition of the ideal end-member, Na(Li1.5Al1.5)Al6(BO3)3Si6O18(OH)4. Substitution from elbaite and schorl/dravite toward R 1−x + R 3 3+ R 6 3+ (BO3)3Si6O18O3−x(OH)1+x is very extensive and may be complete. Substitution toward R 1−x + R 3 3+ R 6 3+ (BO3)3Si6O18O3−x(OH)1+x results in improved local charge balance. The mean deviation $${\Delta \zeta \left( {\text{O}} \right)}$$ from oxygen charge saturation $$\left( {\zeta \left( {\text{O}} \right) = 2.0} \right)$$ is at a maximum in end-member schorl, dravite and elbaite. Substitutions (1) and (2) progressively decrease $${\Delta \zeta \left( {\text{O}} \right)}$$ but substitution (1) does so more effectively, which may explain its predominance in nature. However, alkali-defective end-members appear to be unstable regardless of $${\Delta \zeta \left( {\text{O}} \right)}$$ . Substitution (3) in the elbaites cannot be discussed on the basis of charge balance considerations at present due to the lack of structural information on proton-rich species.

Influence of the X-site composition on tourmaline’s crystal structure: investigation of synthetic K-dravite, dravite, oxy-uvite, and magnesio-foitite using SREF and Raman spectroscopy

Abstract: The crystal structures of synthetic K-dravite [XKYMg 3 Z Al 6 T Si6O18(BO3) 3 V (OH) 3 W (OH)], dravite [XNaYMg 3 Z Al 6 T Si6O18(BO3) 3 V (OH) 3 W (OH)], oxy-uvite [XCaYMg 3 Z Al 6 T Si6O18(BO3) 3 V (OH) 3 W O], and magnesio-foitite [X☐Y(Mg2Al)ZAl 6 T Si6O18(BO3) 3 V (OH) 3 W (OH)] are investigated by polarized Raman spectroscopy, single-crystal structure refinement (SREF), and powder X-ray diffraction. The use of compositionally simple tourmalines characterized by electron microprobe analysis facilitates the determination of site occupancy in the SREF and band assignment in the Raman spectra. The synthesized K-dravite, oxy-uvite, and magnesio-foitite have significant Mg–Al disorder between their octahedral sites indicated by their respective average 〈Y–O〉 and 〈Z–O〉 bond lengths. The Y- and Z-site compositions of oxy-uvite (YMg1.52Al1.48(10) and ZAl4.90Mg1.10(15)) and magnesio-foitite (YAl1.62Mg1.38(18) and ZAl4.92Mg1.08(24)) are refined from the electron densities at each site. The Mg–Al ratio of the Y and Z sites is also determined from the relative integrated peak intensities of the Raman bands in the O–H stretching vibrational range (3250–3850 cm−1), producing values in good agreement with the SREF data. The unit cell volume of tourmaline increases from magnesio-foitite (1558.4(3) A3) to dravite (1569.5(4)–1571.7(3) A3) to oxy-uvite (1572.4(2) A3) to K-dravite (1588.1(2) A3), mainly due to lengthening of the crystallographic c-axis. The increase in the size of the X-site coordination polyhedron from dravite (Na) to K-dravite (K) is accommodated locally in the crystal structure, resulting in the shortening of the neighboring O1–H1 bond. In oxy-uvite, Ca2+ is locally associated with a deprotonated W (O1) site, whereas vacant X sites are neighbored by protonated W (O1) sites. Increasing the size of the X-site-occupying ion does not detectably affect bonding between the other sites; however, the higher charge of Ca and the deprotonated W (O1) site in oxy-uvite are correlated to changes in the lattice vibration Raman spectrum (100–1200 cm−1), particularly for bands assigned to the T 6O18 ring. The Raman spectrum of magnesio-foitite shows significant deviations from those of K-dravite, dravite, and oxy-uvite in both the lattice and O–H stretching vibrational ranges (100–1200 and 3250–3850 cm−1, respectively). The vacant X site is correlated with long- and short-range changes in the crystal structure, i.e., deformation of the T 6O18 ring and lengthening of the O1–H1 and O3–H3 bonds. However, X-site vacancies in K-dravite, dravite, and oxy-uvite result only in the lengthening of the neighboring O1–H1 bond and do not result in identifiable changes in the lattice-bonding environment.

Structure and photoluminescence characteristics of mixed nickel–chromium oxides nanostructures

Abstract: In this work, nickel–chromium-layered double hydroxide (Ni(II)–Cr(III)LDH) is prepared via co-precipitation method at room temperature with 1:2:3 molar ratio of CrCl3·6H2O: NiCl2·6H2O: NaCl using sodium hydroxide as a precipitating agent. Ni(II)–Cr(III) LDH is synthesized in the absence and in the presence of functionalized amino-organic compounds such as acetamide, glycine, and urea. The ratio between CrCl3·6H2O: NiCl2·6H2O: NaCl: acetamide, glycine or urea was 1:2:3:6. The mixed nickel–chromium oxide nanoparticles are prepared by the calcination of Ni(II)–Cr(III) LDHs at 600 ℃ for 2.5 h. Ni(II)–Cr(III) LDHs and mixed Ni(II)–Cr(III) oxides nanoparticles are characterized by several techniques including FTIR, TGA, XRD, FESEM, HRTEM, and PL. Functionalized amino-organic compounds improve the thermal stability in the order of glycine > urea > acetamide. Also, it affects photoluminescence PL intensity which indicates a marked reduction in electron–hole recombination with the highest photocatalytic activity compared to visible light-driven H2 and O2 evolution. The resulting mixed Ni(II)–Cr(III) oxides particles have an amorphous structure and a relatively uniform size of below 10 nm.

Tourmaline studies through time: contributions to scientific advancements

Abstract: Tourmaline studies have been an integral part of science and scientific exploration for centuries and continue to flourish today. In the 19th century, the curious pyroelectric and piezoelectric properties of this mineral attracted the attention of scientists who considered tourmaline central to a grand unification of the theories of heat, electricity and magnetism. The common occurrence of tourmaline in granites and granitic pegmatites was widely known at that time, but, subsequently, tourmaline was discovered in a great range of igneous, metamorphic and sedimentary rocks and a variety of ore deposits, including hydrothermal systems. The chemical complexity of this mineral became more fully established and “appreciated” by the end of the 19th century. In the earlyand mid-20th century, tourmaline studies greatly expanded as a consequence of the (1) exploration of wider ranges of geological settings, (2) development of instrumentation to characterize the chemical and physical properties of minerals and (3) the applications that derived from these studies. In clastic sedimentary rocks, tourmaline was identified as one of the most important heavy minerals and became a means to estimate maturity of the clastic sediment, to determine provenance and to make stratigraphic correlations. The crystallography of tourmaline was more fully understood and the overall structure and general structural formula was known by the 1960–1970’s. Applications of tourmaline relied originally on its piezoelectric properties that became increasingly important during the 20th century. One application, developed after World War I, was the detection and measurement of conventional and atomic explosion pressures based on tourmaline’s piezoelectric properties. Tourmaline studies have expanded in breadth and greatly increased in number since 1977, when micro-analytical and crystallographic/spectroscopic instrumentation became widely available. Petrologically, tourmaline has become a valuable petrogenetic indicator mineral in rocks and sediments due to its occurrence in most rock types, its extreme P–T range of stability, from the near surface to the deepest levels of the crust, its capacity to attain a chemical signature during the evolution of the rock in which it is formed, its ability to retain that chemical imprint, and its capability to provide specific information on the time, temperature and fluid history of its host rock. More recent studies have greatly expanded the conceptual framework of its internal structure and have dramatically increased the number of tourmaline species from 4 to 33. The future of tourmaline studies is promising with many new and exciting possibilities that will continue to influence scientific inquiry well into the future.