J. Appl. Cryst.の発刊に際して

Zolensky ME, and McSween, HY Jr (1988) Aqueous alteration. In Meteorites and the Early Solar System (JF KCITIdge, MS Matthews cds) Univ. of Ari zona, Tucson, 114143 Zoicnsky ME, Score R, Schutt JW, Clayton RN, Mayeda TK (1989a) Lea County 001, an H5 chondrile, and Lea County 002, an ungrouped type 3 chondrite. Meteoritics 24:227-232 Zolensky ME, Barrett R, Prinz M (l989b) Petrography and mineralogy of Yamalo-86720 and Belgica7904. 14th Syrup Ant Meteorites 24-26 Zolensky ME, Barrett R, Prinz M (1989c) Petrography, mineralogy and matrix composition of Yamato82162, a new el2 chondrite (abstr). Lunar Planet Sci XXVL1253-1254 Zolensky ME, Prinz M, Lipschutz ME (199 1) Mineralogy and thermal history of Y-82162, Y-86720, B7904, Abstr Symp Antarct Met 16:195-196 Zolensky ME, Hewins RH , ~ittlefehldt DW, Lindstrom MM, Xiao X, Lipschutz ME (1992) Mineralogy, petrology and geochemistry of carbonaceous chondritie clasts in the LEW 85300 polymiet eucrite. Meteoritics 27:596-604 Zolcnsky ME, Barrett T, Browning L (1993) Mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites. Geochim Cosmochim Acta 57:3123-3148 Zolcnsky ME, Weisb~g MK, Buchanan PC, Mittlcfehldt DW (l996a) Mineralogy of carbonaceous chondrite clasts in HED achondrites and the Moon. Met Planet Sci 31 :518-537 Zol ensky ME, Ivanov AV, Yang V, Mittlefehldt DW, Ohsumi K (l996b) The Kaidun meteorite: Mineralogy of an unusual CM 1 lithology. Meteoritics 31 :484-493 Chapter 4

Non-chondritic meteorites from asteroidal bodies

The interaction between mercury (Hg) and selenium (Se) is one of the best known examples of biological antagonism, yet the underlying mechanism remains unclear. This review focuses on the possible pathways leading to the Hg-Se antagonism, with an emphasis on the potential Hg-Se compounds that are responsible for the antagonism at the molecular level (i.e., bis[methylmercuric]selenide, methylmercury selenocysteinate, selenoprotein P-bound HgSe clusters, and the biominerals HgSexS1−x). The presence of these compounds in biological systems has been suggested by direct or indirect evidence, and their chemical properties support their potentially key roles in alleviating the toxicity of Hg and Se (at high Hg and Se exposures, respectively) and deficiency of Se (at low Se exposures). Direct analytical evidences are needed, however, to confirm their in vivo presence and metabolic pathways, as well as to identify the roles of other potential Hg-Se compounds. Further studies are also warranted for the determination of thermodynamic properties of these compounds under physiological conditions toward a better understanding of the Hg-Se antagonism in biota, particularly under real world exposure scenarios.

Mercury-selenium compounds and their toxicological significance: toward a molecular understanding of the mercury-selenium antagonism.

Subcellular distribution of mercury, selenium, silver, copper, zinc, and cadmium was determined in the liver of northern fur seals (Callorhinus ursinus), black-footed albatrosses (Diomedea nigripes), and Dall’s porpoises (Phocoenoides dalli). Mercury, selenium, and silver were preferentially accumulated in nuclear, lysosomal, and mitochondrial fraction with an increase in their hepatic concentrations, whereas copper, zinc, and cadmium were accumulated mainly in cytosol with an increase in the hepatic concentrations for all three species. To gain insight into the existing state of the metals, they were extracted with four extractants—sodium dodecylsulfate (SDS); 2-mercaptoethanol; 2-mercaptoethanol + guanidinium thiocyanate; and copper sulfate (CuSO4)—at several concentrations from nuclear, lysosomal, and mitochondrial fraction in liver from a specimen of northern fur seal. Extraction efficiencies of the metals for 2-mercaptoethanol + guanidinium thiocyanate and CuSO4 were much higher than those for SDS and 2-mercaptoethanol. Also, for all individuals of the three species, metals were extracted by the three extractants—2% SDS; 0.25 mol/L 2-mercaptoethanol + 5 mol/L guanidinium thiocyanate; and 0.1 mol/L CuSO4—from nuclear, lysosomal, and mitochondrial fraction of liver. In the northern fur seals with higher concentration of mercury, the molar ratio of selenium to mercury approached unity in the nonextractable fraction of 0.25 mol/L 2-mercaptoethanol + 5 mol/L guanidinium thiocyanate, suggesting the possible formation of mercuric selenide (HgSe) with increasing hepatic concentration. Because the nonextractable content of mercury and its distribution were larger for black-footed albatross than those for the other two species, it was suggested that the black-footed albatross has a stronger ability to form a stable compound(s) of mercury in the liver. It is notable that the existing state of silver was similar to that of mercury as judged by their subcellular distribution and the extraction tests, suggesting that silver also interacted with selenium in the liver of marine animals used in this study.

Detoxification mechanism of heavy metals in marine mammals and seabirds: interaction of selenium with mercury, silver, copper, zinc, and cadmium in liver.

Polytypic transformations in silicon carbide

The paper reports results of X-ray and neutron structure refnements of four labradorites An 62-An 66 with di-fferent geological histories and di-fferent superstructures. A rapidly quenched crystal collected during the eruption of Surtsey (Iceland) is essentially disordered. Labradorite from massive lava flows of Lake County (Oregon) shows D reflections, and two metamorphic labradorites from the Central Alps display an intermediate plagioclase structure with e reflections. The average structure (c : 7 A) of all four samples converging at R factors of 3-6Vo are virtually identical with well-defined Si/Al and smeared-out oxygen positions. We interpret this as evidence that the di-fferent superstructures consist of periodic stackings of similar basic units probably lssepfling those in 1l anorthite but with diflerent stacking orders. The main intensity contribution to superstructure reflections comes from displacements of oxygens in the superstructures, probably caused by Al-Si ordering. Phase relations are illustrated in a hypothetical TTT diagram in which we summarize results from structure refinements, microstructural observations and changes during experimental heating. At high temperature Qittle undercoqling below the critical temperature) ordering takes place by a nucleation and growth mechanism which produced 1l domains separated by curved APB's (antiphase boundaries) (Lake County). At larger undercooling continuous ordering prevails, giving rise to periodic APB's and satellites in the diffraction pattern.

/pdf/the-average-structure-of-an-62-66-labradorite-44t1rc5m3v.pdf

The average structure of An 62–66 labradorite

Sea mammals are known to contain high concentrations of mercury and selenium especially in the liver with no apparent symptoms of poisoning. We examined the chemical form of mercury and sele- nium in the liver of striped dolphin, Stenella coeruleoalba. Neither mercury nor selenium could be extract- ed with acetone, 80% ethanol or 0.2 M ammonium acetate. The residue after extraction was digested most effectively with alkaline protease, resulting in solubilization of almost all the material (99% by weight) but still leaving a small amount of insoluble material (1%), which contained 80% of mercury and 66% of sele- nium of the original amount. This insoluble material was subjected to transmission electron microscopic analysis, X-ray microanalysis, X-ray diffraction analysis and elemental analysis, which revealed that the material contained spherical crystals of Hg(S~ .34, Seo 66) with 5-10 nm in diameter as a major component. These crystals may be the final detoxification product of mercury.

Striped dolphin detoxificates mercury as insoluble Hg(S, Se) in the liver

Thermal transformation of SiC crystals were studied experimentally. Needle-like 2H crystals prepared by the gaseous cracking method were heated up to 1,200-2,300•Ž, and when brought down to room temperature, their X-ray oscillation photographs were taken. Diffuse streaks appeared along the c*direction in the diffraction pattern of the specimen heated at 1,600•Ž, and then spots due to 3C emerged along the streaks. At 1,900•Ž, spots due to 4H appeared and at 2,000•Ž those due to 6H. The spots from 3C dis appeared at 2,100•Ž. Throughout these changes, the external form of the speci men remained unchanged and most part of 2H persisted. At 2,300•Ž, only spots observed were those from 2H and 6H. From these findings, it was concluded that 3C, 4H, 6H and probably 2H are thermodynamically stable

THERMAL TRANSFORMATIONS IN SiC CRYSTALS

Petalite, LiAlSi4O10, can be interpreted as a layer silicate. Folded [Si205]-layers are linked by Li und Al tetrahedra. The crystal structure of a natural petalite was refined using neutron diffraction. The refinement of the centrosymmetric structure (space group Ρ 2/a) converged to an R factor of 3.6 % for 830 observed reflections. The site occupancies of Li, Al and Si in the tetrahedra were directly refined. The result shows that these three cations are perfectly ordered. The crystal used in neutron diffraction was also studied by transmission electron microscopy. In dark-field images, antiphase domains were observed. The antiphase vector is 5 [100] and the boundary planes are parallel to (001) and (IOT). The formation of the antiphase domains is closely related with Li and Al ordering. Oriented intergrowths of two high temperature phases and original low-petalite resulted during a heat experiment.

Kristallographische Untersuchungen eines Petalits mittels Neutronenbeugung und Transmissionselektronenmikroskopie

Tridymite from the Steinbach meteorite is monoclinic with cell dimensions: a 18.54, b 5.00, c 23.83 A, β 105.70° and space group C2⁄c or Cc. Its diffraction pattern shows an extremely large number of structural absences, leading to pseudo-orthorhombic superlattice with cell dimensions A 51.86, B 30.00, C 49.20 A. The method of twin analysis (Ito and Sadanaga, 1970) was applied uniquely to derive a crystal lattice from the twin pattern. Pseudohexagonal twinning about the [-201] row of the true monoclinic lattice satisfactorily accounts for these unusual structural extinctions. The symmetry of the twin is represented by the six-color symmetry symbolism. A possible mechanism of twin formation is proposed, based on the recently determined low tridymite structure.

Tokuhei Tagai

Papers

The average structure of An 62–66 labradorite

Striped dolphin detoxificates mercury as insoluble Hg(S, Se) in the liver

THERMAL TRANSFORMATIONS IN SiC CRYSTALS

Kristallographische Untersuchungen eines Petalits mittels Neutronenbeugung und Transmissionselektronenmikroskopie

Twinning of tridymite from the Steinbach meteorite