Lunar and Planetary Science XLVIII (2017) 2237.pdf

SYNTHESIS OF Na-BEARING WHITLOCKITE AND IMPLICATIONS FOR INTERPRETATION OF EXTRATERRESTRIAL PHOSPHATE MINERALS. C. T. Adcock1 and E. M. Hausrath1, 1University of Nevada, Las Vegas, Department of Geoscience, 4505 S. Maryland Pkwy., Las Vegas, Nevada, 89154. [email protected]

Introduction: Mars possesses as much as 10 times Methods: Na-whitlockite synthesis experiments more phosphorus than Earth [1], and in martian were based on previously published methods [13, 16]. meteorites much of it is held in the primary phosphate Following that method, solutions of MgNO3·6H2O, minerals merrillite (Ca9(Na,Fe,Mg)(PO4)7) and FeS (in one experiment), and Ca5(PO4)7OH were chlorapatite (Ca5(PO4)3Cl) [2]. These phosphate created with 18.2 Ωohm water directly in a Parr acid minerals are important as potential indicators of digestion vessel. We modified the method by adding a magma evolution and volatile budgets in late stage source of Na+ cations to create a specific Na/Mg molar magmas of planetary bodies [3-9]. In addition, altered ratio in solution depending on the particular and secondary phosphate minerals can be used as experiment. Once the solution was mixed, the pH was indicators of past surface and near surface aqueous adjusted using H3PO4 to a value of <2.8. The vessel environments and water budgets on Mars [10-12]. was then sealed and incubated at 240 °C for one week. These minerals are also important in martian Five experiments were run in total. Four of the astrobiological studies as the source of potentially experiments were Mg-whitlockite syntheses with a Na bioessential P [11]. source (no source of Fe) while the final experiment Merrillite is of particular interest because it does additionally contained FeS. not occur in any significant amounts on Earth outside After incubation, vessels were quick cooled in a of biologic systems [13], but it is a common phosphate water bath. Crystalline material recovered from the mineral in many meteorites [2, 14], including martian vessels was inspected by optical microscopy to identify and lunar meteorites. The relative paucity of merrillite whitlockite and any other phases present (typically on Earth compared to extraterrestrial materials monetite, metallic opaques presumed to be oxides, and suggests it may hold clues to important differences hydroxyapatite). Whitlockite from the experiments was between Earth and other bodies such as Mars. then mounted in epoxy mounts and analyzed by However, this paucity also means that physical Electron Microprobe (EMP) at the UNLV Electron samples of merrillite for laboratory study can be Microprobe and Imaging Lab (EMiL) to determine difficult to obtain. chemistry and derive stoichiometry. Merrillite can be synthesized from the mineral Results: Optical microscopy inspection of whitlockite (Ca9(Fe,Mg)(PO3OH)(PO4)6) by heating it synthetic materials confirmed synthetic crystal to >1000 °C [13-16]. Whitlockite and merrillite form a morphologies consistent with whitlockite in all solid-solution, with whitlockite being the H-bearing synthesis experiments. Yields of whitlockite from the end-member and merrillite being H-free. Whitlockite is experiments were generally lower than syntheses of itself relatively rare, but methods have been developed Mg- and Fe-only containing whitlockite. Crystal size to synthesize the mineral hydrothermally [13, 16] and was also generally smaller and impurities (additional synthetic whitlockite has been successfully used to phases) were greater. EMP results from the synthetic produce merrillite for planetary studies [13, 15, 16]. whitlockite confirmed stoichiometries that are One of the challenges to using synthetic whitlockite consistent with whitlockite (Tables 1 and 2) as well as to produce merrillite has been synthesizing whitlockite incorporation of Na+ into the synthetic whitlockite with cation chemistry similar to that of merrillite in (Table 1). Increases in the Na:Mg molar ratio in the martian and lunar materials. The goal of this research experiments appear to enhance Na+ incorporation in a therefore has been to produce whitlockite and consistent manner (Figure 1). The addition of FeS to merrillite with cation chemistry comparable to that the experiment also appears to enhance Na+ found in lunar and martian materials. In previous work incorporation. we developed methods to produce whitlockite and Discussion and Ongoing Work: Our results merrillite with Mg2+ and Fe2+ content similar to indicate Na-bearing whitlockite can be synthesized extraterrestrial merrillite [13]. However, merrillite also using hydrothermal methods. The Na+ contents from often contains Na+, a cation that does not generally our experiments are low compared to natural merrillite occur in natural whitlockite, and here we discuss in martian meteorites, but are similar to Na contents in results of experiments to synthesize Na-bearing merrillite found in lunar rocks and meteorites. In whitlockite for merrillite synthesis. particular, whitlockite from the experiment including Lunar and Planetary Science XLVIII (2017) 2237.pdf

FeS, with the highest Na+ content, is close to merrillite similar to martian merrillite. Method optimization is found in Lunar sample 14161, sub-sample 7350 [17]. also planned in order to improve overall yields. Very high Na:Mg molar ratios appear to be Finally, we plan to synthesize Mars-relevant Na- required for significant Na+ incorporation. Past bearing merrillite from the produced whitlockite. The experiments have shown that whitlockite syntheses ability to economically and quickly synthesize a using high concentration solutions have low success chemically accurate analog of an extraterrestrial rates, so this may be the reason for relatively lower mineral will make an otherwise limited resource whitlockite yields. The addition of an Fe2+ source openly available for research that requires physical seems to enhance Na+ incorporation, although this is samples. based on a single experiment. In addition, future Acknowledgements Funding for this work was provided optimization similar to that which we have performed by NASA Grant No. NNX15AL54G, and by the for Mg whitlockite [11, 13] may increase mineral University of Nevada, Las Vegas. We also wish to yields, purity, and Na concentrations. thank Courtney Bartlett and Angela Garcia for UNLV laboratory support and Minghua Ren of EMiL

References: [1] Wanke, H. and Dreibus, G., (1988) Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences. 325 (1587): p. 545-557. [2] McSween, H. and Treiman, A.H., (1998) Planetary Materials, p. F1-F53. [3] Patiño Douce, A.E., et al., (2011) Chemical Geology. 288 (1): p. 14-31. [4] Filiberto, J. and Treiman, A.H., (2009) Geology. 37 (12): p. 1087-1090. [5] Gross, J., et al., (2013) Meteoritics & Planetary Science. 45 (5): p. 854-871. [6] McCubbin, F.M. and Nekvasil, H., (2008) American Mineralogist. 93 (4): p. 676-684. [7] Patiño Douce, A.E. and Roden, M., (2006) GCA 70 (12): p. 3173-3196. [8] Gross, J., et al., (2013) Earth and Planetary Science Letters. 369: p. 120-128. [9] Figure 1. Wt. % of Na2O incorporated into synthetic McCubbin, F.M., et al., (2014) American Mineralogist. 99 whitlockite vs. Na:Mg molar ratios in synthesis solutions. (7): p. 1347-1354. [10] Hurowitz, J.A., et al., (2006) Journal of Geophysical Research. 111. [11] Adcock, C., et al., (2013) Table 2. Stoichiometries based on EMP analyses Nature Geoscience. 6 (10): p. 824-827. [12] Adcock, C.T. ID Stoichiometry and Hausrath, E.M., (2015) Astrobiology. 15 (12): p. 1060- MGS-08 Ca8.97Mg0.98(PO3OH)(PO4)6.01 1075. [13] Adcock, C.T., et al., (2014) American EXT 15 Ca Mg Fe (PO OH)(PO ) 8.97 0.36 0.60 3 4 5.97 Mineralogist. 99 (7): p. 1221-1232. [14] Jolliff, B.L., et al., EXT 17 Ca Mg Na (PO OH)(PO ) 8.95 0.94 0.02 3 4 6.02 (1993) Geochimica et Cosmochimica Acta. 57 (16): p. 4069- EXT 18 Ca8.94Mg0.96Na0.04(PO3OH)(PO4)6.02 4094. [15] Gopal, R., et al., (1974) Canadian Journal of EXT 19 Ca8.87Mg0.92Na0.07(PO3OH)(PO4)6.06 Chemistry-Revue Canadienne De Chimie. 52 (7): p. 1155- EXT 20 Ca8.81Mg0.92Na0.08(PO3OH)(PO4)6.08 EXT 21 Ca8.90Mg0.91Fe0.03Na0.13(PO3OH)(PO4)6.01 1164. [16] Hughes, J.M., et al., (2008) American Mineralogist. 93 (8-9): p. 1300-1305. [17] Jolliff, B.L., et al., Future work includes further experiments to (2006) American Mineralogist. 91 (10): p. 1583-1595. try an achieve Mg2+, Fe2+, and Na+ whitlockite contents

Table 1. EMP analyses of synthesized whitlockite MGS-08 EXT 15 EXT 17 EXT 18 EXT 19 EXT 20 EXT 21*** Na:Mg* - - 4:1 13:1 33:1 46:1 46:1

Na2O BD BD 0.07 0.11 0.19 0.23 0.37 FeO 0.01 3.96 0.02 0.04 0.03 0.02 0.19 CaO 47.69 46.19 47.38 47.26 46.90 46.84 46.87 MgO 3.72 1.35 3.59 3.66 3.50 3.52 3.45 P2O5 47.15 45.40 47.08 46.97 47.19 47.59 46.68 SO3 0.16 0.91 0.19 0.17 0.14 0.18 0.51 H2O** 0.86 0.86 0.86 0.86 0.86 0.86 0.86 Total 99.60 98.67 99.20 99.07 98.81 99.25 98.94 Note: MGS-08 and EXT-15 are Na+ free syntheses for comparison. *Molar ratio in synthesis solution. **Assumed from [16]. ***Fe-bearing synthesis. BD=Below Detection Limit.