Kenji Hagiya

Mineralogy and Petrology of Comet 81P/Wild 2 Nucleus Samples

The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.

Radar-Enabled Recovery of the Sutter’s Mill Meteorite, a Carbonaceous Chondrite Regolith Breccia

The Meteor That Fell to Earth In April 2012, a meteor was witnessed over the Sierra Nevada Mountains in California. Jenniskens et al. (p. 1583) used a combination of photographic and video images of the fireball coupled with Doppler weather radar images to facilitate the rapid recovery of meteorite fragments. A comprehensive analysis of some of these fragments shows that the Sutters Mill meteorite represents a new type of carbonaceous chondrite, a rare and primitive class of meteorites that contain clues to the origin and evolution of primitive materials in the solar system. The unexpected and complex nature of the fragments suggests that the surfaces of C-class asteroids, the presumed parent bodies of carbonaceous chondrites, are more complex than previously assumed. Analysis of this rare meteorite implies that the surfaces of C-class asteroids can be more complex than previously assumed. Doppler weather radar imaging enabled the rapid recovery of the Sutter’s Mill meteorite after a rare 4-kiloton of TNT–equivalent asteroid impact over the foothills of the Sierra Nevada in northern California. The recovered meteorites survived a record high-speed entry of 28.6 kilometers per second from an orbit close to that of Jupiter-family comets (Tisserand’s parameter = 2.8 ± 0.3). Sutter’s Mill is a regolith breccia composed of CM (Mighei)–type carbonaceous chondrite and highly reduced xenolithic materials. It exhibits considerable diversity of mineralogy, petrography, and isotope and organic chemistry, resulting from a complex formation history of the parent body surface. That diversity is quickly masked by alteration once in the terrestrial environment but will need to be considered when samples returned by missions to C-class asteroids are interpreted.

The modulated structure of synthetic Co-åkermanite, Ca2CoSi2O7

Diffraction patterns of synthetic Co-akermanite, Ca 2 CoSi 2 O 7 , reveal distinct satellite reflections at room temperature. An incommensurate modulation in this material has been determined by five-dimensional refinement pf the structure. The basic structure is tetragonal P42 1 m, unit-cell dimensions a=7.8417 (6), c=5.0249 (3) A, V=308.99 A 3 , Z=2, M r =307.26, D m =3.307 (4) g cm -3 at 293 K, D x =3.302 g cm -3 , Mo Kα with graphite monochromator, μ=47.7 cm -1 , F(000)=302, R=0.049 for 734 unique reflections

Development of a System to Analyse the Structure of a Submicrometre-Sized Single Crystal by Synchrotron X-ray Diffraction

A system has been developed for the analysis of the structure of a submicrometer-sized single crystal using synchrotron radiation (SR) at the Photon Factory (PF), KEK. The Laue method combined with an imaging plate was employed for the collection of diffracted intensities. To reduce background, the experiment was carried out in a vacuum and with a very thinly collimated incident X-ray beam. The system has been shown to reach a level where a molybdenum sphere with diameter as small as 0.8 Ixm was found to be twinned and the volume ratio of the twin domains was determined, together with an isotropic temperature factor, which was comparable with the value determined in the same experiment on another single-crystal sphere of almost the same size. It was in good agreement with that determined by a powder diffraction study. The present study showed that any single crystal detectable under an optical microscope can be analysed and, further, that the diffraction intensities from a crystal with volume of 0.02 Ix m 3, which is composed of 10 9 atoms, can be detected.

Commensurate structure of Ca2CoSi2O7, a new twinned orthorhombic structure

The crystal structure of the commensurate phase of Ca2CoSi2O7, dicalcium cobalt disilicate, has been derived from the modulated structure described in (3 + 2)-dimensional space. The structure is orthorhombic P21212; a = 23.510 (4), b = 23.510 (4), c = 5.025 (1) A (at 170 K), Z = 18. Since the crystal is twinned and the apparent diffraction symmetry is 4/mmm, the parameters were refined by a newly developed least-squares program for the refinement of twinned crystals. The structure is essentially similar to the known structure of the melilite group, but with regular arrangement of the bundles along [001] formed with four arrays of the sixfold coordinated Ca polyhedra and an array of CoO4 tetrahedra. The distribution of the bundles found in the present structure is different from that reported by Riester et al. [(2000), Z. Kristallogr. 215, 102–109].

Two-dimensional incommensurately modulated structure of (Sr0.13Ca0.87)2CoSi2O7 crystals

The incommensurate structure of (Sr(0.13)Ca(0.87))(2)CoSi(2)O(7) at room temperature has been determined from single-crystal X-ray diffraction data. The compound has a non-centrosymmetric tetragonal basic cell of a = 7.8743 (4) and c = 5.0417 (2) A with the space group P4;2(1)m. The refinements of the basic structure converged to R = 0.038 for 757 main reflections. The two-dimensional incommensurate structure is characterized by the wavevectors q(1) = 0.286 (3)(a* + b*) and q(2) = 0.286 (3)(-a* + b*), where a*, b* are the reciprocal lattice vectors of the basic structure. With the (3 + 2)-dimensional superspace group P(p4mg)(P4;2(1)(m)), the refinements converged to R = 0.071 for 1697 observed reflections (757 main and 940 satellite reflections). The structure is described in terms of displacement of the atoms, rotation, distortion of CoO(4) and SiO(4) tetrahedra, and the partial ordering of the Sr and Ca atoms accompanied with the modulation. Correlated evolution of these features throughout the crystal gives rise to various oxygen coordination around Ca/Sr. Comparison of the derived modulated structure to that of Ca(2)CoSi(2)O(7) clarified that the partial substitution of Ca by large alkaline-earth atoms such as Sr should decrease the distortion of the polyhedra around the cations.

Andreyivanovite: A second new phosphide from the Kaidun meteorite

Abstract Andreyivanovite (ideally FeCrP) is another new phosphide species from the Kaidun meteorite, which fell in South Yemen in 1980. Kaidun is a unique breccia containing an unprecedented variety of fragments of different chondritic as well as achondritic lithologies. Andreyivanovite was found as individual grains and linear arrays of grains with a maximum dimension of 8 μm within two masses of Fe-rich serpentine. In one sample, it is associated with Fe-Ni-Cr sulfides and florenskyite (FeTiP). Andreyivanovite is creamy white in reflected light, and its luster is metallic. The average of nine electron microprobe analyses yielded the formula Fe(Cr0.587Fe0.150V0.109Ti0.081Ni0.060Co0.002)P. Examination of single grains of andreyivanovite using Laue patterns collected by in situ synchrotron X-ray diffraction (XRD), and by electron-backscatter diffraction revealed it to be isostructural with florenskyite; we were unable to find single crystals of sufficient quality to perform a complete structure analysis. Andreyivanovite crystallizes in the space group Pnma, and has the anti-PbCl2 structure. Previously determined cell constants of synthetic material [a = 5.833(1), b = 3.569(1), and c = 6.658(1) Å] were consistent with our XRD work. We used the XPOW program to calculate a powder-XRD pattern; the 5 most intense reflections are d = 2.247 (I = 100), 2.074 (81), 2.258 (46), 1.785 (43), and 1.885 Å (34). Andreyivanovite is the second new phosphide to be described from the Kaidun meteorite. Andreyivanovite could have formed as a result of cooling and crystallization of a melted precursor consisting mainly of Fe-Ni metal enriched in P, Ti, and Cr. Serpentine associated with andreyivanovite would then have formed during aqueous alteration on the parent asteroid. It is also possible that the andreyivanovite could have formed during aqueous alteration; however, artificial FeTiP has been synthesized only during melting experiments, at low oxygen fugacity, and there is no evidence that a hydrothermal genesis is reasonable.

Variation of large-scale regularity in modulated structures of Ca2CoSi2O7 studied by a simulation method.

The period of two-dimensional modulation in Ca2CoSi2O7 varies with temperature (q = 0.285-1/3). The change in the modulated structure with the variation of q has been clarified by the construction of the structures using various q values and the modulation amplitudes determined at 293 K [q = 0.2913 (1), tetragonal]. The features of the modulated structures are characterized by the formation of CaO6 polyhedra and the variable distribution of bundles along the c-axis, composed of four arrays of CaO6 polyhedra and an array of CoO4 tetrahedra. The formation of octagonal arrangements of the bundles is a typical feature of the structures in the incommensurate phase. Large-scale regularities with sizes much larger than the modulation wavelength are also formed in the structures.

Development of a microarea diffraction system by polychromatic synchrotron radiation with the Laue method

Microarea diffraction equipment has been developed with a micropinhole and an imaging plate using the Laue method combined with polychromatic synchrotron radiation. The crystal structure of 8 μm diam area of olivine [(Mg,Fe)2SiO4] grain included in a thin section of meteorite was successfully refined based on the intensities of Laue spots.

Characterization of 5‐μm‐sized icosahedral chemical vapor deposited diamond by synchrotron x‐ray diffraction with Laue method

A system for analyzing and refining the crystal structure of a submicrometer‐sized specimen has been developed at the Photon Factory, KEK, employing a Laue method with an imaging plate. The system was evaluated using two molybdenum spheres with diameters of 0.8 μm and 0.27 μm3 in volume. The result showed that the isotropic temperature factors of both spheres were successfully refined, and that one of the samples was found to be twinned. The smaller domain of the twin was determined to be 0.02 μm3 in volume, which means that the smaller domain is composed of only 109 Mo atoms. The system was applied to a 5‐μm‐sized icosahedral CVD diamond as a first application. Analysis of several Laue patterns revealed that the sample is composed of more than 17 domains. Among them, 16 domains are twinned with each other, and the mode of twinning is of the spinel twin type.