A. Beran

Molluscan shell evolution with review of shell calcification hypothesis

Biomineralization research on mollusc shells has mostly focused on nacre formation. Chitin, silk fibroin protein, and acidic macromolecules are important components for shell formation. Although the principle concept behind shell calcification was developed many years ago, the individual components have not been well scrutinized. Besides that, Mollusca are the second largest invertebrate phylum, but comprehensive biochemical research involving a comparison of different taxa is still rare. This study reconsiders the above three components with adding some biochemical data of aculiferans. The presence of chitin in polyplacophorans sclerites was confirmed by IR and pyrolysis GC/MS. DMMB staining data inferred that sulphated groups present in aplacophoran cuticle but not in polyplacophorans cuticle. These insight suggested importance of comparison between acuriferans and conchiferans.

A model of the OH positions in olivine, derived from infrared-spectroscopic investigations

Polarized infrared (IR) spectroscopy of olivine crystals from Zabargad, Red Sea shows the existence of four pleochroic absorption bands at 3,590, 3,570, 3,520 and 3,230 cm−1, and of one non pleochroic band at 3,400 cm−1. The bands are assigned to OH stretching frequencies. Transmission electron microscopy (TEM) shows no oriented intergrowths in this olivine; it is concluded that OH is structural. On the basis of the pleochroic scheme of the absorption spectra it is proposed that [□O(OH)3] and [□O2(OH)2] tetrahedra occur as structural elements, assuming that the vacancies are on Si sites. If M2 site vacancies were assumed [SiO3(OH)] and [SiO2(OH)2] tetrahedra occur as structural elements.

Single crystal infrared spectra in the range of OH fundamentals of paragenetic garnet, omphacite and kyanite in an eklogitic mantle xenolith

SummarySingle crystals of paragenetic garnet (gt), omphacite (cpx) and kyanite (ky) were isolated from an eclogite xenolith from the Zagadochnaya kimberlite, Yakutia (grospydite Z13) and studied by polarized FTIR-microspectrometry in the OH valence vibrational region and by microprobe analyses. The coexisting minerals are homogeneous with respect to major and minor elements and have compositions near gross49pyr26alm20uvar4 (gt), jad45dio47hed6kos2 (cpx) and ky>97. Single crystal spectra show one νOH-band for gt at 3630 cm−1 (halfwidth ca. 100 cm−1) which is very likely caused by vibrations of tetrahedral (OH)4-4− clusters replacing SiO44− tetrahedra. Cpx shows one strong, but weakly pleochroic band at 3464 cm−1 (halfwidth ca. 160 cm−1) and a weak satellite band centered at 3620 cm−1) with a distinct pleochroism. Ky OH spectra exhibit two sets of weak sharp pleochroic bands, a triplet, characteristic for high pressure ky, at 3439, 3410, 3387 cm−1) and a doublet at 3279, 3264 cm−1) (halfwidths ca. 10 cm−1) From integral and linear absorbances in the unpolarized spectra defect-hydroxyl contents in the three coexisting minerals were estimated and found near O.OX wt% H2O. The distribution scheme of hydrogen in the paragenetic minerals was evaluated to be cky < ccpx ≪< cgt.ZusammenfassungAus einer Granat (Gt)-Omphacit (Cpx)-Kyanit (Ky) Paragenese eines Eklogit Xenoliths aus dem Zagadochnaya Kimberlit, Jakutien (Grospydit Z13), wurden Einkristalle isoliert und mit polarisierter FTIR-Mikrospektrometrie im OH Valenzschwingungsbereich und mit der Elektronenstrahl-Mikrosonde untersucht. Die koexistierenden Minerale sind hinsichtlich ihrer Haupt- und Nebenelemente homogen und haben Zusammen setzungen von etwa Gross49Pyr26Alm20Uvar4 (Gt), Jad45Dio47Hed6Kos2 (Cpx) and Ky>97 Einkristallspektren von Gt zeigen eine νOH-Bande bei 3630 cm−1) (Halbwerts breite ca. 100 cm−1) die wahrscheinlich von Schwingungen tetraedrischer (OH)44− Gruppen, die SiO44− Tetraeder ersetzen, herrührt. Cpx zeigt eine starke, aber schwach pleochroitische Bande bei 3464 cm−1 (Halbwertsbreite ca. 160 cm−1) and eine schwache, deutlich pleochroitische Satellitenbande bei 3620 cm−1) Ky OH Spektren zeigen zwei Gruppen von schwachen, scharfen pleochroitischen Banden, ein fur Hochdruck Ky charakteristisches Bandentriplett bei 3439, 3410, 3387 cm−1) and ein Bandendublett bei 3279, 3264 cm−1) (Halbwertsbreiten ca. 10 cm−1) Aus den integralen and linearen Extinktionen der nicht-polarisierten Spektren wurde der Defekt-Hydroxyl Gehalt der drei koexistierenden Minerale abgeleitet and mit O.OX Gew% H2O festgelegt. Das Verteilungsschema des Wasserstoffs kann in der Mineralparagenese mit cKy < cCpx ≪ cGt angegeben werden.

OH defects in forsterite

Polarized FTIR spectra of near endmember forsterite single crystals from Pamir, Tadzikistan show the existence of sharp strongly pleochroic absorption bands in the region of the OH stretching fundamental. Bands centered at 3674/3624, 3647/3598 and 3640/ 3592 cm-1 are attributed to OH dipoles oriented parallel to [100]. An OH band doublet at 3570/3535 cm-1 shows both, a strong absorption parallel to [100] and a strong component parallel to [001]. On the basis of the pleochroic scheme and under the assumption of vacancies on Si- and M-sites it is proposed that O1 is partially replaced by OH defects pointing to the vacant Si-site. O3 is donator oxygen of OH dipoles lying near the O3-O1 tetrahedral edge or roughly pointing to a vacant M2-site. Also O2 can act as donator oxygen of an OH group oriented along the O2-O3 edge of a vacant M1 octahedron. The splitting of the bands is explained by the presence of Fe2+ in cation sites surrounding the OH defects.

A model of water allocation in alkali feldspar, derived from infrared-spectroscopic investigations

Polarizedinfrared (IR) spectra of sanidine crystals from Volkesfeld, Eifel show the existence of two broad pleochroic absorption bands at 3,400 and 3,050 cm−1. Because overtones near 5,150 cm−1 were observed, the former bands are assigned to OH stretching frequencies of H2O molecules. On the basis of the pleochroic scheme of the bands it is proposed that H2O molecules occur as structural constituents entering theM site of the sanidine structure; the plane of the H2O molecules lies parallel to the symmetry plane.

Dehydration and Structural Development of Mullite Precursors: An FTIR Spectroscopic Study

Abstract Mullite type, I and III precursors were prepared by a sol-gel process using tetraethoxysilane and aluminum sec.-butoxide as starting materials. The precursors were treated by 15 h heating steps in intervals of 100°C from 200 to 1000°C. Type III precursors are characterised by a more discontinuous decrease of the analytical water content compared to that of type I precursors. The FTIR powder spectra of the preheated precursors show weak absorption bands at 5160 and 4540 cm −1 which are due to H 2 O and OH combination modes, thus proving the presence of both, H 2 O molecules and OH groups as structural components of the precursors. (H 2 O, OH) stretching modes are centered at around 3430 cm −1 and H 2 O bending modes at 1635 cm −1 . The deconvolution of the stretching mode bands reveals non-bridging and bridging H 2 O molecules and OH groups. Close similarities in the pattern of the 1400–400 cm −1 vibrational region between type I and III precursors exist up to preheating temperatures of 800°C. Significant differences are evident at temperatures of 900°C, where the spectrum of the type III precursor still corresponds to that at 800°C, while the type I precursor reveals a spectrum with features present in the spectrum of mullite. Bands centered around 1110 and 1010 cm −1 are assigned to Si–O stretching vibrations of the SiO 4 tetrahedral units and are strongly shifted in 900°C treated type I precursors to higher wavenumbers. This band shift is a strong indication for an increasing degree of network condensation and for changes in the Si–O distances to tetrahedra dimensions similar to those of mullite. A significant absorption around 860 cm −1 is assigned to Al–O stretching modes of AlO 4 tetrahedral units, a band around 570 cm −1 is assigned to Al–O stretching vibrations of AlO 6 octahedral units. A slightly decreasing intensity of this band with increasing preheating temperatures, along with a strongly increasing intensity of the 860 cm −1 band demonstrates a clear preference of Al for a four-fold coordinated structural position in the precursors preheated at high temperatures. This process is correlated to the dehydration process occurring in the medium- to high-temperature field of network condensation starting at around 400°C.

OH groups in nominally anhydrous framework structures: An infrared spectroscopic investigation of danburite and labradorite

The pleochroic behaviour of two nominally anhydrous structurally similar minerals, danburite and An59 labradorite, was investigated in the region of the OH stretching frequencies. Danburite shows a sharp absorption band at 3540 cm−1, labradorite shows a broad band with an absorption maximum at 3230 cm−1. On the basis of the pleochroic scheme of theinfrared (IR) absorption spectra it is proposed that the OH dipoles in danburite are located within the symmetry plane showing a distinct orientation parallel to [010]; the OH groups in labradorite are oriented approximately perpendicular to (001). The proposed models are in accordance with bond valence calculations showing that in both framework structures the most deficient oxygens, O5 in danburite and OCm in labradorite, are partially replaced by OH.

Water in enstatite from Mid-Atlantic Ridge peridotite: Evidence for the water content of suboceanic mantle?

We present the first water concentration data for oceanic mantle peridotite. The rocks come from the Mid-Atlantic Ridge and were sampled by drilling during Leg 153 of the Ocean Drilling Program. Earlier studies of peridotite xenoliths suggest that orthopyroxene is the most important host of water in the upper mantle. However, an unresolved question is whether the measured water content in orthopyroxene is equal to its original concentration in the mantle or possibly lower because of decompression-related water loss. Our investigations of oceanic mantle rocks yield water contents in orthopyroxene in the range between 160 and 270 ppm by weight (wt). These new data, compared with those from xenoliths, experimental studies, and geophysical investigations, imply that the measured values reflect the original mantle contents. The preservation of mantle water contents is ascribed to an exhumation mechanism that provides for cooling during ascent of the suboceanic mantle slices.

Spectroscopic and structural properties of synthetic micas on the annite-siderophyllite binary: Synthesis, crystal structure refinement, Mössbauer, and infrared spectroscopy

Abstract The effect of the incorporation of Al-Tschermak’s molecule to the trioctahedral potassium mica annite {K}[Fe3]O10(OH)2 on local and average structure has been investigated by hydrothermal synthesis, structure refinement of X-ray powder diffraction data, Mössbauer and infrared spectroscopy. The various types of brackets indicate different structural sites. Samples with compositions {K}[Fe3-xAlx]O10(OH)2 were prepared by hydrothermal techniques. The maximum solubility of Al3+ is limited to x = 0.92 at 500 °C and to x = 0.82 at 700 °C. The main factor controlling the substitution limits is the ditrigonal distortion of the tetrahedral rings. Lattice parameters decrease linearly with increasing Al3+ content of the mica. A considerable decrease of M2-O and nearly no change of M1-O bond lengths with increasing Al3+ contents is indicative of preferred occupation of the M2 site by [Al3+]. Changes in K-O distances are also very pronounced and reflect the ditrigonal distortion of the tetrahedral sheet. The bimodal ferrous quadrupole splitting distribution (QSD) in annite, extracted from Mössbauer spectra, becomes narrower and more centered around 2.60 mm/s with increasing Al3+ contents, and its evolution suggests an increasing deviation from ideal octahedral coordination of Fe by O, illustrated by the increasing octahedral flattening angle y. The population of individual QSD components proves that it is impossible to resolve cis and trans M-sites in micas by Mössbauer spectroscopy. In the hydroxyl stretching region, up to 7 bands are observed in the infra-red spectra which correspond to OH groups adjacent to 3 Fe2+ (N-bands), to OH groups coordinated by Fe2+, Al3+, and Fe3+ (I-bands) and to configurations having one octahedral vacancy (V-bands). N- and I-type bands are shifted toward lower wavenumbers with increasing Al3+ content because of increasing OH···Otet interactions.

A Mössbauer and X-ray diffraction study of annites synthesized at different oxygen fugacities and crystal chemical implications

A refined set of Mössbauer parameters (isomer shifts, quadrupole splittings, Fe2+/Fe3+ ratios) and lattice parameters were obtained from annites synthesized hydrothermally at pressures between 3 and 5 kbars, temperatures ranging from 250 to 780° C and oxygen fugacities controlled by solid state buffers (NNO, QMF, IM, IQF). Mössbauer spectra showed Fe2+ and Fe3+ on both the M1 and the M2 site. A linear relationship between Fe3+ content and oxygen fugacity was observed. Towards low Fe3+ values this linear relationship ends at ≈10% of total iron showing that the Fe3+ content cannot be reduced further even if more reducing conditions are used. This indicates that in annite at least 10% Fe2+ are substituted by Fe3+ in order to match the larger octahedral layer to the smaller tetrahedral layer. IR spectra indicate that formation of octahedral vacancies plays an important role for charge balance through the substitution 3 Fe2+ → 2 Fe3+ + ▪(oct).