Characterization of mineral coatings associated with a Pleistocene-Holocene rock art style: The Northern Running Figures of the East Alligator River region, western Arnhem Land, Australia

This data article contains mineralogic and chemical data from mineral coatings associated with rock art from the East Alligator River region. The coatings were collected adjacent to a rock art style known as the “Northern Running Figures” for the purposes of radiocarbon dating (doi:10.1016/j.jasrep.2016.11.016; (T. Jones, V. Levchenko, P.L. King, U. Troitzsch, D. Wesley, 2017) [1]). This contribution includes raw and processed powder X-ray Diffraction data, Scanning Electron Microscopy energy dispersive spectroscopy data, and Fourier Transform infrared spectral data.This research was supported by Australian Research Council grants to King (FT130101524 and DP150104604). The Centre for Advanced Microscopy is supported by the Australian Microscopy and Microanalysis Research Facility (AMMRF)

Iron cation vacancies in Pt(iv)-doped hematite

Platinum-doping of hematite (α-Fe2O3) is a popular method to increase the performance of hematite in photoelectrochemical applications. The precise mode of Pt incorporation is however unclear, as it can occur as Pt0, Pt2+ or Pt4+, either on the surface, as dispersed inclusions, or as part of the hematite crystal lattice. These different Pt-doping varieties can have major effects on the hematite performance. Here, we employ a high-pressure synthesis method assisted by silicate liquid flux to grow Pt-doped hematite crystals large enough for elemental analysis by wavelength dispersive spectroscopy (WDS). We find that the total cations are lower than the expected 2 atoms per formula unit, and together with Fe, they are inversely correlated with Pt contents. Linear regressions in compositional space reveal that the slopes are consistent with 4Fe3+ = 3Pt4+ + VFe as the charge-balanced substitution mechanism. Therefore, Pt4+-doping of hematite at high oxygen fugacities, which does not allow Fe2+ to form, will lead to removal of Fe and formation of cation vacancies. Our hematite also contains significant Al3+, Ti4+ and Mg2+, raising the possibility of fine tuning the hematite properties by co-doping with other elements. Photoelectrochemical performance of cation vacancy bearing hematite is experimentally understudied and is a potentially promising future field of study

Automated analysis of pottery by QEM-EDS: A case study from Mansiri, Sulawesi

The analysis of raw materials and manufacturing techniques is central to the investigation of pottery assemblages. While various analytical techniques exists, petrography generally remains the go-to method to analyse the fabric of pottery. It combines relatively cheap and simple sample preparation protocol with the ability to yield very detailed information related to provenance and manufacturing technique. Here, we test the utility of performing QEM-EDS on archaeological pottery from the Mansiri site, Sulawesi, to complement petrographic observations. We identify the main non-plastic inclusions as plagioclase, quartz, calcic amphibole, iron oxides and volcanic rock fragments, consistent with the pottery being made locally. Quantitative analysis of inclusion size and direction suggests that the non-plastic inclusions were not manually added, and that in contrast to other Neolithic Sulawesi sites, coiling with beating/paddle and anvil was used to manufacture the pots

Ti02-Doped Zirconia: Crystal Structure, Monoclinic-Tetragonal Phase Transition, and the New Tetragonal Compound Zr3Ti08

Zirconia samples with up to 27 mol% TiO2 were synthesized at low and elevated pressures, significantly extending the range of ZrO 2-TiO2 solid solution compared with previous crystal structure studies of monoclinic and tetragonal zirconia (<17.5 mol%). Crystal structure data collected by powder X-ray diffraction (XRD) at ambient conditions reveal that the solid solution of TiO2 in monoclinic zirconia (baddeleyite structure, P21/c) is limited to about 25 mol%, where the tetragonal compound Zr3TiO8 forms. Changes in the monoclinic crystal structure with increasing TiO2 can be understood in the light of the nearing monoclinic-tetragonal phase change. Unit-cell dimensions a and b become near identical, cell angle β starts to drop toward 90°, and atom positions start to change toward those of the tetragonal cell. The cation coordination polyhedron in the monoclinic structure becomes increasingly distorted, and bond-valence sums worsen. The transition from the monoclinic to the tetragonal lattice with increasing TiO2 is not smooth however, but shows a significant jump in many of the parameters, in line with the first-order character of this transition. The previously unknown inorganic compound Zr3TiO8 has a structure related to that of tetragonal zirconia (P42/nmc), whereby weak superstructure reflections indicate that the structure is ordered and has a doubled c-dimension. Zr3TiO8 has the unit-cell dimensions a = 5.0317(4) Å and c = 10.4273(7) Å, space group (I-42m), and is isostructural with the compound Zr3GeO8, with Ti 4+ in tetrahedral coordination and Zr4+ in eightfold coordination. The stabilization of tetragonal Zr3TiO8 at ambient conditions depends strongly on the cooling rate, which has to be slow enough (e.g., 1°C/min) to allow for ordering to occur. Rapid quenching (e.g., ∼140°C/s) of the same composition results in monoclinic zirconia. The lowering of the tetragonal-monoclinic phase transition to ambient conditions near 25 mol% TiO2 is in good agreement with extrapolations from previous studies. The relatively coarse grain size (< 20 μm) of the Zr3TiO8 crystals suggest that the tetragonal structure was not retained because of grain-size effects, but was stabilized predominantly by crystal structure adjustments based on cation size. Broadening and shortening of selected XRD peaks especially upon grinding suggests that tetragonal Zr3TiO8, depending on cooling rate and degree of ordering, may be retained metastably at room temperature, and is thus a potential candidate for TZP ceramics

The crystal structure and thermodynamic properties of titanite solid-solution Ca(Ti,A1)(O,F)SiO₄

Two journal articles in back pocket: Crystal structural changes in titanite along the join TiO-A1F / Ulrike Troitzsch ...[et al.] -- The synthesis and crystal structure of CaA1FSiO4, the A1-F analog of titanite / Ulrike Troitzsch and David J. Elli

High-PT study of solid solutions in the system Zr02-Ti02: The stability of srilankite

The ZrO2-TiO2 phase diagram was studied with synthesis experiments between 1200°C and 1650°C, 1 atm and 28 kbar, investigating the effect of pressure on the compositions of rutile [TiO2], zirconia [ZrO2] , and zirconium titanate [(Zr,Ti)2O4) solid solu

The synthesis and crystal structure of CaAlFSiO4 , the Al-F analog of titanite

Aluminum-rich titanites [Ca(Ti,Al)(O,F)SiO4] with X(Al) > 0.53 [X(Al)=Al/(Al+Ti)], including the pure end-member CaAlFSiO4, were synthesized for the first time in a high-pressure experimental study. The crystal structure of CaAlFSiO4 was determined by Rietveld analysis of an X-ray powder diffraction pattern. CaAlFSiO4 is monoclinic, belongs to the space group A2/a, and has the unit-cell dimensions a = 6.9149(2) Å, b = 8.5064(1) Å, c = 6.4384(2) Å, and β = 114.684(2)°. The unit-cell volume is less than 93% of CaTiOSiO4, which is consistent with the natural occurrence of Al-rich titanite in high-P rocks. Although previous studies suggested that titanite with X(Al) > 0.5 is possibly not stable, this study demonstrates that complete solid solution occurs between CaTiOSiO4 and CaAlFSiO4. The similarity of the crystal structures of titanite and CaAlFSiO4 explains why in natural Al-rich titanite the end-member CaAlFSiO4 generally dominates over the hypothetical end-member CaAlOHSiO4, which under geological conditions is stable in a different crystal structure

Thermodynamic properties and stability of AIF-bearing Titanite CaTiOSi04-CaAIFSi04

Calorimetric and experimental data on AlF-bearing titanite are presented that yield thermodynamic properties of CaAlFSiO4, as well as activity-composition relations of binary titanite CaTiOSiO4-CaAlFSiO4. The heat capacity of synthetic CaAlFSiO4 was measured with differential scanning calorimetry between 170 and 850 K: Cp = 689.96 - 0.38647T+2911300T-2 - 8356.1T-0.5 +0.00016179T2 Based on low-temperature heat capacity calculations with lattice vibrational theory (Debye model), the calorimetric entropy of CaAlFSiO4 can be expected to lie between 104.7 and 118.1 J mol-1 K-1. The temperature of the P21/a to A2/a phase change was determined calorimetrically for a titanite with XA1=0.09 (Ttransition = 390 K). The decrease of the transition temperature at a rate of about 11 K per mo1% CaAlFSiO4 is in good agreement with previous TEM investigations. The displacement of the reaction anorthite + fluorite = CaAlFSiO4 in the presence of CaTiOSiO4 was studied with high P-T experiments. Titanite behaves as a non-ideal, symmetrical solid-solution. The thermodynamic properties of CaAlFSiO4 consistent with a multi-site mixing model are: Enthalpy of formation (elements)dfH0 = -2740.8 ±3.0 kJmo1-1 Standard state entropy S0 = 104.9±1.1 Jmo1-1 K-1 Margules parameter [WH-TWs] = 13.6±0.4 Jmo1-1 The pressure dependence of the Margules parameter (Wv) was determined from the excess volume of mixing based on XRD measurements (214±18 J mo1-1 Kbar-1), as well as refined from the piston-cylinder experimental results (198±114 J mo1-1 kbar-1), demonstrating consistency between crystal structure data and thermodynamic properties. The stability of AlF-bearing titanite Ca(Ti,Al)(O,F)SiO4 was investigated by thermodynamic modelling in the system Ca-Al-Si-Ti-O-F-H-C and subsystems. The petrogenetic grids are in good agreement with natural mineral assemblages, in that very Al-rich titanite (XA1>0.65±0.15) is generally absent because it is either unstable with respect to other phases, or its stability field lies outside the P-T conditions realised on Earth. The grids explain both the predominant occurrence of natural Al-rich titanite at high metamorphic grade such as eclogite facies conditions, as well as its scarcity in blueschist facies rocks. Wide spacing of the Al-isopleths for titanite of many high-grade assemblages prevents their use as geobarometers or thermometers. The instability of end-member CaAlFSiO4 with respect to other phases in most assemblages modelled here is consistent with the hypothesis that the presence of structural stresses in the crystal lattice of CaAlFSiO4 influences its thermodynamic stability. The titanite structure is not well suited to accommodate Al and F instead of Ti and O, causing the relatively high Gibbs free energy of CaAlFSiO4, manifested in its standard state properties. Thus, the increasing amount of CaAlFSiO4 along the binary join is the reason why titanite with XA1>0.65±0.15 becomes unstable in most petrogenetic grids presented here. The compositional limit of natural titanite (XA1≈0.54) probably reflects the point beyond which the less stable end member begins to dominate the solid-solution, affecting both crystal structure and thermodynamic stability

The Zr02-Ti02 phase diagram

The ZrO2-TiO2 phase diagram was determined experimentally between 800 and 1200°C, 1 atm, extending our knowledge of this system to temperatures previously inaccessible for equilibrium experiments due to sluggish kinetics. The crystallization of the orde

A preliminary study into the Lavongai rectilinear earth mounds: an XRD and phytolith analysis

This paper reports a pilot study undertaken at the Lavongai rectilinear earth mounds site in New Hanover, New Ireland Province, Papua New Guinea. The objective of the study was to determine whether the mounds were formed as part of a prehistoric agricultural system. X-ray Diffraction and phytolith analyses were used on a series of sediment samples from a test pit excavated into one of the Lavongai mounds. The phytolith results indicate a change from forest species in the lowest samples to grass species in the highest samples and the presence of a variety of plant species recorded in the ethnography of medicinal plants. The XRD results indicate that the sediments throughout the depth of the mound have a similar origin, suggesting that the changes in phytoliths do not represent changes in the source of the sediments. It is proposed that the phytolith results reflect four phases of gardening practices beginning between c. 3000 bp and c. 4000 bp