Gokce Ustunisik

Solid solution in the fluorapatite-chlorapatite binary system: High-precision crystal structure refinements of synthetic F-Cl apatite

Abstract Apatite sensu lato, Ca10(PO4)6(F,OH,Cl)2, is the tenth most abundant mineral on Earth, and is fundamentally important in geological processes, biological processes, medicine, dentistry, agriculture, environmental remediation, and material science. The steric interactions among anions in the [0,0,z] anion column in apatite make it impossible to predict the column anion arrangements in solid solutions among the three end-members. In this work we report the measured atomic arrangements of synthetic apatite in the F-Cl apatite binary with nominal composition Ca10(PO4)6(F1Cl1), synthesized in vacuum at high temperature to minimize both hydroxyl- and oxy-component of the apatite. Four crystals from the high-temperature synthesis batch were prepared to assess the homogeneity of the batch and the precision of the location of small portions of an atom in the apatite anion column by single-crystal X-ray diffraction techniques. Crystals were ground to spheres of 80 μm diameter, and full-spheres of MoKα diffraction data were collected to θ = 33°, with average redundancies >16. Final R1 values ranged from 0.0145 to 0.0158; the lattice parameters ranged from a = 9.5084(2)-9.5104(3), c = 6.8289(3)-6.8311(2) Å. Based on this study, solid solution in P63/m apatites along the F-Cl join is attained by creation of an off-mirror fluorine site at (0,0,0.167), a position wherein the fluorine atom relaxes away from its normal position within the {00l} mirror plane in P63/m apatites; that relaxation is coupled with relaxation of a chlorine atom at the adjacent mirror plane away from the off-mirror fluorine, allowing acceptable F-Cl distances in the anion column. There are a total of four partially occupied anion positions in the anion column, including two for fluorine [(0,0,1/4) and (0,0,0.167)] and two for chlorine [(0,0,0.086) and (0,0,0)]; the chlorine site at the origin was previously postulated but not observed in calcium apatite solid solutions.

A novel technique for fluorapatite synthesis and the thermodynamic mixing behavior of F-OH apatite crystalline solutions

Abstract Successful synthesis of fluorapatite has been achieved through ion-exchange between NIST hydroxlyapatite SRM 2910a and optical-grade fluorite. Additional intermediate F-OH apatite compositions were made through ion-exchange between the newly synthesized fluorapatite and the original hydroxylapatite. Based on solution calorimetric data collected on seven fluorapatite-hydroxlyapatite crystalline solutions at 50 °C in 20.0 wt% HCl under isoperibilic conditions, fluorine-rich series members display ideal thermodynamic behavior, whereas hydroxyl-rich compositions show negative enthalpies of F-OH mixing. Unit-cell volumes for the series are linear with composition. Relative to enthalpy and volume, therefore, there are no energy barriers to complete solid solution between the F and OH end-members.

Low-pressure crystallization of a volatile-rich lunar basalt: A means for producing local anorthosites?

Abstract The presence of anorthosite in the lunar highlands containing plagioclase that is compositionally less calcic than plagioclase in the ferroan anorthosites cannot be readily explained by the current lunar paradigm in which lunar anorthosite was produced as a floatation cumulate in the lunar magma ocean. Phase-equilibrium experiments were conducted to investigate whether such anorthosite could arise locally from crystallization of aluminous magma at shallow levels within the lunar crust. The experiments were conducted on a synthetic analog of Cl-, F-, and S-bearing aluminous highland basalt 14053 at pressures of approximately 1 bar and ƒO₂ at ~QIF. Pyroxene and plagioclase (An93-89) saturation occurs early, and with continued crystallization, the residual liquid evolves to a silica-poor, halogen-, Fe-, and Ti-rich melt with a computed density of >3.1 g/mL. This liquid remains higher in density than the plagioclase over the crystallization interval, providing the possibility of plagioclase/ melt separation by liquid draining. A model is proposed in which “alkali” anorthosite, consisting of sodic anorthite or bytownite, coupled with underlying pyroxenite (or harzburgite) is produced locally during crystallization of plagioclase from “Al-rich” magmas at or within roughly a kilometer of the lunar surface. In this model, segregation of plagioclase would be attained by settling of ferromagnesian minerals to the bottom of a shallow magma chamber, and draining of low-viscosity, low-silica, Fe-Ti-K-REE-P-enriched residual basaltic melt to deeper regions of the crust, or into topographic lows. Such residual melt may be represented by magma compositions similar to some of the intermediate- to high-Ti mare basalts. This model would provide a mechanism that can account for the more “alkali” anorthosite identified in widespread isolated locales on the Moon and allow for variable ages for such anorthosite that may extend to ages of the mare basalts.

Pilot Program for Teaching Earth Science in New York

During the 2009–2010 school year, 40% of New York City (NYC) Earth science teachers were not certified to teach Earth science [New York State Education Department (NYSED), 2011]. This highlights a longstanding shortage of certified teachers, which persists today and prevents many schools from offering courses on the subject, thus diminishing student opportunities to study or embark on careers in Earth science. More generally, the paucity of qualified, effective science teachers hinders student achievement in science, technology, engineering, and mathematics (STEM), and research has consistently shown that improving the quality of teaching substantially increases achievement in STEM-related fields [National Science Board, 2007]. With only 36% of NYC 8th graders scoring at or above the basic level of proficiency in science and with even lower scores for African-American and Hispanic students [Livingston and Wirt, 2005], the need for more qualified science teachers is clear.

Experimental investigation of F and Cl partitioning between apatite and Fe-rich basaltic melt at 0 GPa and 950–1050 °C: Evidence for steric controls on apatite-melt exchange equilibria in OH-poor apatite

Abstract Apatite-melt partitioning experiments were conducted in a Deltech vertical-quench 1-bar furnace at 0 GPa and 950–1050 °C using an Fe-rich basaltic starting composition. Each experiment had a unique F:Cl ratio to assess the partitioning of F and Cl between apatite and melt, and the oxygen fugacity of all experiments was between IW and IW-1. Apatite-melt partitioning of F and Cl along the F-Cl binary join is investigated in particular to assess the effect of non-ideal mixing of apatite X-site components. The quenched melt and apatite from each experiment were analyzed by electron probe microanalysis. Several of our experiments exhibited evidence of silicate liquid immiscibility (SLI), so we also evaluated the effect of SLI on the partitioning of F and Cl between apatite and melt in those experiments. The F-Cl exchange equilibria between apatite and melt were variable with KDCl−FAp−melt

New insights into the processes controlling compositional zoning in plagioclase

\begin{array}{} \displaystyle \rm{{\it K}_{D_{Cl-F}}^{Ap-melt}} \end{array}

Experimental investigation of condensation predictions for dust-enriched systems

values in the range of 0.08–0.21 across the F-Cl join. The KDCl−FAp−melt

Magmatic Degassing in Planetary Bodies: What Apatite can Tell Us

\begin{array}{} \displaystyle \rm{{\it K}_{D_{Cl-F}}^{Ap-melt}} \end{array}

Using Apatite to Assess Volatile Contents of Primary Lunar Magmas: Potential Pitfalls

values decreased with decreasing F in apatite and melt. Notably, we did not observe evidence that SLI has a first-order effect on the behavior of F and Cl partitioning between apatite and melt. The observed drop in KDCl−FAp−melt

Trace element partitioning between plagioclase and melt: An investigation of the impact of experimental and analytical procedures: IMPACT OF ANALYTICAL PROCEDURES ON D

\begin{array}{} \displaystyle \rm{{\it K}_{D_{Cl-F}}^{Ap-melt}} \end{array}