David C. Elbert

Comprehensive characterization of skeletal tissue growth anomalies of the finger coral Porites compressa

The scleractinian finger coral Porites compressa has been documented to develop raised growth anomalies of unknown origin, commonly referred to as “tumors”. These skeletal tissue anomalies (STAs) are circumscribed nodule-like areas of enlarged skeleton and tissue with fewer polyps and zooxanthellae than adjacent tissue. A field survey of the STA prevalence in Oahu, Kaneohe Bay, Hawaii, was complemented by laboratory analysis to reveal biochemical, histological and skeletal differences between anomalous and reference tissue. MutY, Hsp90a1, GRP75 and metallothionein, proteins known to be up-regulated in hyperplastic tissues, were over expressed in the STAs compared to adjacent normal-appearing and reference tissues. Histological analysis was further accompanied by elemental and micro-structural analyses of skeleton. Anomalous skeleton was of similar aragonite composition to adjacent skeleton but more porous as evidenced by an increased rate of vertical extension without thickening. Polyp structure was retained throughout the lesion, but abnormal polyps were hypertrophied, with increased mass of aboral tissue lining the skeleton, and thickened areas of skeletogenic calicoblastic epithelium along the basal floor. The latter were highly metabolically active and infiltrated with chromophore cells. These observations qualify the STAs as hyperplasia and are the first report in poritid corals of chromophore infiltration processes in active calicoblastic epithelium areas.

Aragonite crystallization in primary cell cultures of multicellular isolates from a hard coral, Pocillopora damicornis

The foundation of marine coral reef ecosystems is calcium carbonate accumulated primarily by the action of hard corals (Coelenterata: Anthozoa: Scleractinia). Colonial hard coral polyps cover the surface of the reef and deposit calcium carbonate as the aragonite polymorph, stabilized into a continuous calcareous skeleton. Scleractinian coral skeleton composition and architecture are well documented; however, the cellular mechanisms of calcification are poorly understood. There is little information on the nature of the coral cell types involved or their cooperation in biocalcification. We report aragonite crystallization in primary cell cultures of a hard coral, Pocillopora damicornis. Cells of apical coral colony fragments were isolated by spontaneous in vitro dissociation. Single dissociated cell types were separated by density in a discontinuous Percoll gradient. Primary cell cultures displayed a transient increase in alkaline phosphatase (ALP) activity, to the level observed in intact corals. In adherent multicellular isolate cultures, enzyme activation was followed by precipitation of aragonite. Modification of the ionic formulation of the medium prolonged maintenance of isolates, delayed ALP activation, and delayed aragonite precipitation. These results demonstrate that in vitro crystallization of aragonite in coral cell cultures is possible, and provides an innovative approach to investigate reef-building coral calcification at the cellular level.

Experimental crystallization of gallium: ultrasonic measurements of elastic anisotropy and implications for the inner core

We present ultrasonic measurements of elastic anisotropy in gallium undergoing directional solidification in the presence of imposed thermal gradients, rotation, convection, turbulence, and magnetic fields. Simultaneous in situ measurements of temperature and compressional wave speed are used to track the crystallization front during solidification. We find that individual solidified gallium samples are always polycrystalline and elastically anisotropic, with grains elongated in the solidification direction. The measured compressional wave anisotropy in individual solid samples ranges from 20 to 80% of the single crystal values, depending on experimental conditions. We also find the amount of elastic anisotropy varies with position in an individual sample. Based on ensemble averages from multiple experiments made under similar environmental conditions, we find the direction of elastic anisotropy in the solid is sensitive to the thermal gradient direction, while the amount of anisotropy is most sensitive to the presence or absence of initial nucleation in the melt. Experiments that show average anisotropy have the ultrasonically fast axis aligned with gravity and the thermal gradient. Strongly anisotropic solids result when nucleation grains are present in the initial melt, whereas smaller or zero average anisotropy results when nucleation grains are initially absent. Other externally imposed factors we have examined, such as turbulence and magnetic fields, have either no measurable influence or tend to reduce the amount of anisotropy of the solid. Our results suggest that during crystallization of Earth’s inner core, the orientation of average anisotropy in the newly formed solid is controlled primarily by radial solidification, while the amount of anisotropy may be influenced by pre-existing inner core texture.

Mineralogy, morphology, and textural relationships in coatings on quartz grains in sediments in a quartz-sand aquifer.

Mineralogical studies of coatings on quartz grains and bulk sediments from an aquifer on Western Cape Cod, Massachusetts, USA were carried out using a variety of transmission electron microscopy (TEM) techniques. Previous studies demonstrated that coatings on quartz grains control the adsorption properties of these sediments. Samples for TEM characterization were made by a gentle mechanical grinding method and focused ion beam (FIB) milling. The former method can make abundant electron-transparent coating assemblages for comprehensive and quantitative X-ray analysis and the latter technique protects the coating texture from being destroyed. Characterization of the samples from both a pristine area and an area heavily impacted by wastewater discharge shows similar coating textures and chemical compositions. Major constituents of the coating include Al-substituted goethite and illite/chlorite clays. Goethite is aggregated into well-crystallized domains through oriented attachment resulting in increased porosity. Illite/chlorite clays with various chemical compositions were observed to be mixed with goethite aggregates and aligned sub-parallel to the associated quartz surface. The uniform spatial distribution of wastewater-derived phosphorus throughout the coating from the wastewater-contaminated site suggests that all of the coating constituents, including those adjacent to the quartz surface, are accessible to groundwater solutes. Both TEM characterization and chemical extraction results indicate there is a significantly greater amount of amorphous iron oxide in samples from wastewater discharge area compared to those from the pristine region, which might reflect the impact of redox cycling of iron under the wastewater-discharge area. Coating compositions are consistent with the moderate metal and oxy-metalloid adsorption capacities, low but significant cation exchange capacities, and control of iron(III) solubility by goethite observed in reactive transport experimental and modeling studies conducted at the site.

Incommensurate c-domain superstructures in calcian dolomite from the Latemar buildup, Dolomites, Northern Italy

Abstract Early exposure cap microdolomites (<50 °C) and low-temperature hydrothermal (<177 °C) calcian dolomite crystals from the Latemar buildup, Dolomites, northern Italy, are microstructurally heterogeneous. Selected-area electron-diffraction patterns contain incommensurate superstructure reflections from domains that are approximately 2.5 nm wide. These domains are quasiperiodic with wavelengths of 5 to 20 nm. The scale of these modulations varies with composition of the bulk crystal. Previously described c-domain superstructures in dolomite are reported as commensurate with the host structure; c-diffraction spots are situated exactly halfway between the principal (a and b) reflections. Re-examination of published diffraction patterns reveals that some are actually incommensurate. Individual c-domains are monoclinic and have been interpreted to be more calcium-rich than the host dolomite. Newly recognized c-domains resemble previously described c-domains but are distinct because they are incommensurate with the dolomite host and produce diffraction spots with irrational indices. In samples from the Latemar buildup, the c-axes of the host and modulations are parallel, but the [110] directions are not parallel. Further, the length of c*dolomite ≈ c*superstructure, but the lattice spacing of d110superstructure is more than twice d110dolomite. The superstructure phase is metrically monoclinic and is interpreted to incorporate more calcium than dolomite. Domains are, however, too small to analyze directly. Excess calcium may account for the more than doubling of the domains’ α-dimension relative to that of dolomite. Inclination of the domain lattice relative to the host lattice may vary as a function of calcium content.

Energy-filtered transmission electron microscopy (EFTEM) of intergrown pyroxenes

Abstract It is demonstrated that energy-filtered transmission electron microscope (EFTEM) imaging in a conventional TEM (CTEM), equipped with a field-emission gun (FEG) electron source, can be used to characterize the local chemical distribution in exsolved pyroxenes. EFTEM imaging, which can be performed in one to tens of minutes, yields two-dimensional compositional maps that can have nanometer- scale resolution. The combination of electron energy-loss spectroscopy (EELS) and EFTEM imaging with techniques such as bright-field and dark-field imaging, high-resolution TEM (HRTEM) imaging, energy-dispersive X-ray spectroscopy (EDS), and electron diffraction allows for the chemical and structural characterization of any sample able to withstand the electron beam. EFTEM imaging, HRTEM, and EDS data suggest that the augite →orthopyroxene reaction in the samples examined occurs in two-steps; augite → pigeonite → orthopyroxene. In this two-step process, the chemical and structural components are accomplished separately, suggesting that it is energetically or kinetically favorable to dissociate the two components rather than have them occur simultaneously. This two-step transformation is supported by the pigeonite → orthopyroxene transformation, which appears to be an isothermal martensitic transformation since the pigeonite and orthopyroxene compositions are identical within analytical error.

Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H2O]

Abstract The metatorbernite [Cu(UO2)2(PO4)2·8H2O] structure comprises autunite-type sheets of cornersharing uranyl square bipyramids and phosphate tetrahedra, with the interlayer region occupied by Cu2+ ions and molecular water. Previous studies have shown that heating induces stepwise dehydration and reduction in basal spacing. Structures of the lower hydrates have not been determined previously because suitable single crystals of these phases have yet to be prepared. We have used synchrotron X-ray diffraction data collected during in situ, continuous heating of powdered metatorbernite to elucidate structures of its lower hydrates. Using Rietveld analysis, we have determined that autunite-type sheets remain intact through the first dehydration event above room temperature (onset 102 °C). We have discovered that the second dehydration event (onset 138 °C) triggers a major reconstruction to uranophane-type sheets, composed of chains of edge-sharing uranyl pentagonal bipyramids linked to one another by sharing edges and vertices with phosphate tetrahedra. This reconstruction enables the structure to overcome steric constraints on the minimum possible basal spacing, while maintaining Cu within the interlayer. Four distinct phases have been identified with increasing temperature: Cu(UO2)2(PO4)2·8H2O, space group P4/n, a = 6.96519(23), c = 17.3102(8) Å; Cu(UO2)2(PO4)2·6.1H2O, space group P4/n, a = 6.95510(29), c = 16.6604(9) Å; Cu(UO2)2(PO4)2·3H2O, space group P21, a = 14.4979(23), b = 7.0159(9), c = 6.6312(10) Å, β = 107.585(14)°; and a lower hydrate with monoclinic or triclinic symmetry, a ≈ 6.7, b ≈ 7, c ≈ 11 Å, β ≈ 100°. As shown here, in situ heating experiments and the Rietveld method provide fundamental insights into the crystal chemistry and structural behaviors of the important meta-autunite mineral group.

A tilting procedure to enhance compositional contrast and reduce residual diffraction contrast in energy-filtered TEM imaging of planar interfaces.

This paper systematically demonstrates that energy-filtered transmission electron microscope (EFTEM) images of a planar interface between two single crystals have increased compositional contrast and decreased residual diffraction contrast when the sample is oriented so that the electron beam is parallel to the interface, but not directly on a zone axis. This off-axis orientation reduces diffraction contrast in the unfiltered (and zero-loss) image, which in turn, reduces residual diffraction contrast in single energy-filtered TEM (EFTEM) images, thickness maps, jump-ratio images, and elemental maps. Most importantly, this procedure produces EFTEM images that are more directly interpretable and, in most cases, possess superior spatial resolution compared to EFTEM images acquired directly on a zone axis.

Dolomite microstructures and reaction mechanisms of dolomitization on the triassic Latemar buildup, Dolomites, northern Italy

The wavelengths of nanometer-scale structural modulations in calcium-rich dolomite on the Latemar buildup, Dolomites, northern Italy vary as a function of composition, which is controlled by the temperature of dolomitizing fluids, and contact time with these fluids. Dolomites formed at the highest temperatures are the most magnesian and those formed at the lowest temperatures are the most calcian. The wavelengths of structural modulations, which are visible in brightfield and high-resolution transmission electron microscope images, increase with increasing temperature of formation. Long wavelength modulations are associated with more magnesium rich dolomite that formed at high temperatures.Three generations of dolomite, formed under subaerial sedimentary to subsurface hydrothermal conditions, partially replace Triassic Latemar limestones. Early exposure cap dolomite (52 to 57 mole % CaCO3) formed at earth surface temperatures and is host to mottles and diffuse modulations with wavelengths of 2 to 7.5 nm. Subsurface hydrothermal dolomite, formed by platform-scale circulation of hot Triassic seawater, comprises a kilometer-scale mushroom-shaped body of massive replacement dolomite and saddle dolomite cement that crosscuts platform sediments (Wilson et al. 1990; Hardie et al. 1991). Massive replacement dolomite from the stem consists of dolomite breccia and saddle dolomite cement. Saddle dolomite cements (49 to 55 mole % CaCO3) formed at high temperatures are host to sharp modulations with wavelengths of 7.5 to 15 nm and ribbon microstructures (1 to 2.5 nm across). Dolomite breccias (52 to 56 mole % CaCO3) are modulated; modulations wavelengths are 5 to 20 nm. Dolomites from the cap of the dolomite body, formed at lower temperatures than those in the stem, are more calcium rich, (51 to 58 mole % CaCO3), and are host to modulations with wavelengths of 0.5 to 12.5 nm.Incommensurate superstructure reflections have been recognized in SAED patterns of calcium rich dolomite from the Latemar buildup. Incommensurate c-reflections have been observed approximately halfway between the principal reflections in the [110]* and [014]* directions. Superstructure reflections overlap the a- and b-reflections of the host dolomite and extend asymmetrically toward the center of the diffraction pattern. The c-reflections are elongated perpendicular to the structural modulations and are produced by quasiperiodic domains (less than approximately 2.5 nm wide) with wavelengths of 5 to 20 nm. The superstructure phase associated with these extra reflections has smaller reciprocal lattice dimensions than the sublattice, hence larger unit cell dimensions. The superstructure phase is metrically monoclinic and is interpreted to incorporate more calcium than the host dolomite, as suggested by previous workers (cf. Reeder and Wenk 1979; Gunderson and Wenk 1981; Reeder 1981, 1983; Wenk and Zhang 1985; Van Tendeloo et al. 1985; Reeder and Prosky 1986; Reeder et al. 1990; Reksten 1990a; Wenk et al. 1991; Reeder 1992; Ward and Reeder 1992).