Stable isotope evidence for ca. 2.7-Ga-old Archean cap carbonates from the Dharwar Supergroup, southern India

Carbon isotope compositions of carbonate rocks from similar to 2.7-Ga-old Neoarchean Vanivilas Formation of the Dharwar Supergroup presented earlier by us are re-evaluated in this study, besides oxygen isotope compositions of a few silica dolomite pairs. The purpose of such a revisit assumes significance in view of recent field evidences that suggest a glaciomarine origin for the matrix-supported conglomerate member, the Talya conglomerate, which underlies the carbonate rocks of the Vanivilas Formation. An in-depth analysis of carbon isotope data reveals preservation of their pristine character despite the rocks having been subjected to metamorphism to different degrees (from lower greenschist to lower amphibolite facies). The dolomitic member of Vanivilas Formation of Marikanive area is characterized by highly depleted delta C-13 value (up to -5 parts per thousand VPDB) and merits as the Indian example of ca. 2.7-Ga-old cap carbonate. This inference is further supported by estimated low temperature of equilibration documented by a few silica dolomite pairs from the Vanivilas Formation collected near Kalche area. These pairs show evidence for oxygen isotopic equilibrium at low temperatures (similar to 0-20 degrees C) with depleted water (delta O-18 = -21 parts per thousand to -15 parts per thousand VSMOW) of glacial origin. We propose that the mineral pairs were deposited during the deglaciation period when the ocean temperature was in its gradual restoration phase. The dolomite of Marikanive area is the first record of cap carbonates from the Indian subcontinent with Neoarchean antiquity.

Preparation of pyrochlore-free PMN by an alternative chemical method

This work reports the synthesis of the MgNb(2)O(6) and the ferroelectric lead magnesium niobate Pb(Mg(1/3)Nb(2/3))O(3) (PMN) using fine precursor powders obtained from a chemical Oxide Precursor Method (OPM). To obtain pyrochlore-free PMN ceramics, the synthesis of the precursor MgNb(2)O(6) powders was studied for 2-25 mol% excess of MgO and 10 mol% excess of PbO. Structural and microstructural properties of the sintered ceramics obtained by the cited method and by the classical columbite method were studied and compared. Results lead to good quality, pyrochlore-free PMN ceramic prepared by OPM, presenting greater grain size if compared with ceramic prepared by columbite method.

Pyrochlore der Pegmatit-Provinz Nazareno, Brasilien

Zusammenfassung:Mit Hilfe einer neuen Formel für die Minerale der Pyrochlor-Gruppe werden sämtliche Endglieder der Na-Ca-Mikrolithe und der Ba-haltigen Mikrolithe aus der Pegmatit-Provinz Nazareno beschrieben: Die Na-reichsten Proben haben nahezu die Idealzusammensetzung eines idealen Pyrochlors, d.h. . Die Ca-reichsten Varietäten weisen maximal auf, wobei der Besetzungsanteil des Ca am A2+ ca. 93% beträgt. Die Ba-haltigen Mikrolithe sind durch eine Defektstruktur gekennzeichnet, wobei für das mögliche Endglied kein Beispiel in den Daten vorliegt. Das Endglied mit dem geringsten Defektcharakter hat folgende Stöchiometrie:

Recommended Nomenclature for the Sapphirine and Surinamite Groups (Sapphirine Supergroup)

Minerals isostructural with sapphirine-1A, sapphirine-2M, and surinamite are closely related chain silicates that pose nomenclature problems because of the large number of sites and potential constituents, including several (Be, B, As, Sb) that are rare or absent in other chain silicates. Our recommended nomenclature for the sapphirine group (formerly-aenigmatite group) makes extensive use of precedent, but applies the rules to all known natural compositions, with flexibility to allow for yet undiscovered compositions such as those reported in synthetic materials. These minerals are part of a polysomatic series composed of pyroxene or pyroxene-like and spinel modules, and thus we recommend that the sapphirine supergroup should encompass the polysomatic series. The first level in the classification is based on polysome, i.e. each group within the supergroup Corresponds to a single polysome. At the second level, the sapphirine group is divided into subgroups according to the occupancy of the two largest M sites, namely, sapphirine (Mg), aenigmatite (Na), and rhonite (Ca). Classification at the third level is based on the occupancy of the smallest M site with most shared edges, M7, at which the dominant cation is most often Ti (aenigmatite, rhonite, makarochkinite), Fe(3+) (wilkinsonite, dorrite, hogtuvaite) or Al (sapphirine, khmaralite); much less common is Cr (krinovite) and Sb (welshite). At the fourth level, the two most polymerized T sites are considered together, e.g. ordering of Be at these sites distinguishes hogtuvaite, makarochkinite and khmaralite. Classification at the fifth level is based on X(Mg) = Mg/(Mg + Fe(2+)) at the M sites (excluding the two largest and M7). In principle, this criterion could be expanded to include other divalent cations at these sites, e.g. Mn. To date, most minerals have been found to be either Mg-dominant (X(mg) > 0.5), or Fe(2+)-dominant (X(Mg) < 0.5), at these M sites. However, X(mg) ranges from 1.00 to 0.03 in material described as rhonite, i.e. there are two species present, one Mg-dominant, the other Fe(2+)-dominant. Three other potentially new species are a Mg-dominant analogue of wilkinsonite, rhonite in the Allende meteorite, which is distinguished front rhonite and dorrite in that Mg rather than Ti or FC(3+) is dominant at M7, and an Al-dominant analogue of sapphirine, in which Al > Si at the two most polymerized T sites vs. Al < Si in sapphirine. Further splitting of the supergroup based on occupancies other than those specified above is not recommended.

The triplite–triploidite supergroup: structural modulation in wagnerite, discreditation of magniotriplite, and the new mineral hydroxylwagnerite

Electron-microprobe analysis, single-crystal X-ray diffraction with an area detector, and high-resolution transmission electron microscopy show that minerals related to wagnerite, triplite and triploidite, which are monoclinic Mg, Fe and Mn phosphates with the formula Me2+ 2PO4(F,OH), constitute a modulated series based on the average triplite structure. Modulation occurs along b and may be commensurate with (2b periodicity) or incommensurate but generally close to integer values (∼3b, ∼5b, ∼7b, ∼9b), i.e. close to polytypic behaviour. As a result, the Mg- and F-dominant minerals magniotriplite and wagnerite can no longer be considered polymorphs of Mg2PO4F, i.e., there is no basis for recognizing them as distinct species. Given that wagnerite has priority (1821 vs. 1951), the name magniotriplite should be discarded in favour of wagnerite. Hydroxylwagnerite, end-member Mg2PO4OH, occurs in pyrope megablasts along with talc, clinochlore, kyanite, rutile and secondary apatite in two samples from lenses of pyrope–kyanite–phengite–quartz-schist within metagranite in the coesite-bearing ultrahigh-pressure metamorphic unit of the Dora-Maira Massif, western Alps, Vallone di Gilba, Val Varaita, Piemonte, Italy. Electron microprobe analyses of holotype hydroxylwagnerite and of the crystal with the lowest F content gave in wt%: P2O5 44.14, 43.99; SiO2 0.28, 0.02; SO3 –, 0.01; TiO2 0.20, 0.16; Al2O3 0.06, 0.03; MgO 48.82, 49.12; FeO 0.33, 0.48; MnO 0.01, 0.02; CaO 0.12, 0.10; Na2O 0.01, –; F 5.58, 4.67; H2O (calc) 2.94, 3.36; –O = F 2.35, 1.97; Sum 100.14, 99.98, corresponding to (Mg1.954Fe0.007Ca0.003Ti0.004Al0.002Na0.001)Σ=1.971(P1.003Si0.008)Σ=1.011O4(OH0.526F0.474)Σ=1 and (Mg1.971Fe0.011Ca0.003Ti0.003Al0.001)Σ=1.989(P1.002Si0.001)Σ=1.003O4(OH0.603F0.397)Σ=1, respectively. Due to the paucity of material, H2O could not be measured, so OH was calculated from the deficit in F assuming stoichiometry, i.e., by assuming F + OH = 1 per formula unit. Holotype hydroxylwagnerite is optically biaxial (+), α 1.584(1), β 1.586(1), γ 1.587(1) (589 nm); 2V Z(meas.) = 43(2)°; orientation Y = b. Single-crystal X-ray diffraction gives monoclinic symmetry, space group P21/c, a = 9.646(3) Å, b = 12.7314(16) Å, c = 11.980(4) Å, β = 108.38(4) , V = 1396.2(8) Å3, Z = 16, i.e., hydroxylwagnerite is the OH-dominant analogue of wagnerite [β-Mg2PO4(OH)] and a high-pressure polymorph of althausite, holtedahlite, and α- and ε-Mg2PO4(OH). We suggest that the group of minerals related to wagnerite, triplite and triploidite constitutes a triplite–triploidite super-group that can be divided into F-dominant phosphates (triplite group), OH-dominant phosphates (triploidite group), O-dominant phosphates (staněkite group) and an OH-dominant arsenate (sarkinite). The distinction among the three groups and a potential fourth group is based only on chemical features, i.e., occupancy of anion or cation sites. The structures of these minerals are all based on the average triplite structure, with a modulation controlled by the ratio of Mg, Fe2+, Fe3+ and Mn2+ ionic radii to (O,OH,F) ionic radii.

Pore depth evolution of a pyrochlore pellet

The long-term stability of ceramic materials that are considered as potential nuclear waste forms is governed by heterogeneous surface reactivity. Thus, instead of a mean rate, the identification of one or more dominant contributors to the overall dissolution rate is the key to predict the stability of waste forms quantitatively. Direct surface measurements by vertical scanning interferometry (VSI) and their analysis via material flux maps and resulting dissolution rate spectra provide data about dominant rate contributors and their variability over time. Using pyrochlore (Nd2Zr2O7) pellet dissolution under acidic conditions as an example, we demonstrate the identification and quantification of dissolution rate contributors, based on VSI data and rate spectrum analysis. Heterogeneous surface alteration of pyrochlore varies by a factor of about 5 and additional material loss by chemo-mechanical grain pull-out within the uppermost grain layer. We identified four different rate contributors that are responsible for the observed dissolution rate range of single grains. Our new concept offers the opportunity to increase our mechanistic understanding and to predict quantitatively the alteration of ceramic waste forms.

Contrasting microfossil preservation and lake chemistries within the 1200–1000 Ma Torridonian Supergroup of NW Scotland

We acknowledge the Australian Microscopy & Microanalysis Research Facility at the Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, a facility funded by the University, State and Commonwealth Governments. DW acknowledges funding from the European Commission and the Australian Research Council. This is publication number 838 from the Australian Research Council Centre of Excellence for Core to Crust Fluid Systems.

On the affinity of Chuaria–Tawuia complex : a multidisciplinary study

In this study, biometric and structural engineering tool have been used to examine a possible relationship within Chuaria–Tawuia complex and micro-FTIR (Fourier Transform Infrared Spectroscopy) analyses to understand the biological affinity of Chuaria circularis Walcott, collected from the Mesoproterozoic Suket Shales of the Vindhyan Supergroup and the Neoproterozoic Halkal Shales of the Bhima Group of peninsular India. Biometric analyses of well preserved carbonized specimens show wide variation in morphology and uni-modal distribution. We believe and demonstrate to a reasonable extent that C. circularis most likely was a part of Tawuia-like cylindrical body of algal origin. Specimens with notch/cleft and overlapping preservation, mostly recorded in the size range of 3–5 mm, are of special interest. Five different models proposed earlier on the life cycle of C. circularis are discussed. A new model, termed as ‘Hybrid model’ based on present multidisciplinary study assessing cylindrical and spherical shapes suggesting variable cell wall strength and algal affinity is proposed. This model discusses and demonstrates varied geometrical morphologies assumed by Chuaria and Tawuia, and also shows the inter-relationship of Chuaria–Tawuia complex. Structural engineering tool (thin walled pressure vessel theory) was applied to investigate the implications of possible geometrical shapes (sphere and cylinder), membrane (cell wall) stresses and ambient pressure environment on morphologically similar C. circularis and Tawuia. The results suggest that membrane stresses developed on the structures similar to Chuaria–Tawuia complex were directly proportional to radius and inversely proportional to the thickness in both cases. In case of hollow cylindrical structure, the membrane stresses in circumferential direction (hoop stress) are twice of the longitudinal direction indicating that rupture or fragmentation in the body of Tawuia would have occurred due to hoop stress. It appears that notches and discontinuities seen in some of the specimens of Chuaria may be related to rupture suggesting their possible location in 3D Chuaria. The micro-FTIR spectra of C. circularis are characterized by both aliphatic and aromatic absorption bands. The aliphaticity is indicated by prominent alkyl group bands between 2800–3000 and 1300–1500 cm−1. The prominent absorption signals at 700–900 cm−1 (peaking at 875 and 860 cm−1) are due to aromatic CH out of plane deformation. A narrow, strong band is centred at 1540 cm−1 which could be COOH band. The presence of strong aliphatic bands in FTIR spectra suggests that the biogeopolymer of C. circularis is of aliphatic nature. The wall chemistry indicates the presence of ‘algaenan’—a biopolymer of algae.

Raman spectroscopic study of the mineral arsenogorceixite BaAl3AsO3(OH)(AsO4,PO4)(OH,F)6

Arsenogorceixite BaAl3AsO3(OH)(AsO4,PO4)(OH,F)6 belongs to the crandallite mineral subgroup of the alunite supergroup. Arsenogorceixite forms a continuous series of solid solutions with related minerals including gorceixite, goyazite, arsenogoyazite, plumbogummite and philipsbornite. Two minerals from (a) Germany and (b) from Ashburton Downs, Australia were analysed by Raman spectroscopy. The spectra show some commonality but the intensities of the peaks vary. Sharp intense Raman bands for the German sample, are observed at 972 and 814 cm−1 attributed to the ν1 PO43− and AsO43− symmetric stretching modes. Raman bands at 1014, 1057, 1148 and 1160 cm−1 are attributed to the ν1 PO2 symmetric stretching mode and ν3 PO43− antisymmetric stretching vibrations. Raman bands at 764 and 776 cm−1 and 758 and 756 cm−1 are assigned to the ν3 AsO43− antisymmetric stretching vibrations. For the Australian mineral, the ν1 PO43− band is found at 973 cm−1. The intensity of the arsenate bands observed at 814, 838 and 870 cm−1 is greatly enhanced. Two low intensity Raman bands at 1307 and 1332 cm−1 are assigned to hydroxyl deformation modes. The intense Raman band at 441 cm−1 with a shoulder at 462 cm−1 is assigned to the ν2 PO43− bending mode. Raman bands at 318 and 340 cm−1 are attributed to the (AsO4)3−ν2 bending. The broad band centred at 3301 cm−1 is assigned to water stretching vibrations and the sharper peak at 3473 cm−1 is assigned to the OH stretching vibrations. The observation of strong water stretching vibrations brings into question the actual formula of arsenogorceixite. It is proposed the formula is better written as BaAl3AsO3(OH)(AsO4,PO4)(OH,F)6·xH2O. The observation of both phosphate and arsenate bands provides a clear example of solid solution formation.

Raman spectroscopic study of the hydroxy-phosphate mineral plumbogummite PbAl3(PO4)2(OH,H2O)6

Plumbogummite PbAl3(PO4)2(OH,H2O)6 is a mineral of environmental significance and is a member of the alunite-jarosite supergroup. The molecular structure of the mineral has been investigated by Raman spectroscopy. The spectra of different plumbogummite specimens differ although there are many common features. The Raman spectra prove the spectral profile consisting of overlapping bands and shoulders. Raman bands and shoulders observed at 971, 980, 1002 and 1023 cm−1 (China sample) and 913, 981, 996 and 1026 cm−1 (Czech sample) are assigned to the ν1 symmetric stretching modes of the (PO4)3−, at 1002 and 1023 cm−1 (China) and 996 and 1026 cm−1 to the ν1 symmetric stretching vibrations of the (O3POH)2− units, and those at 1057, 1106 and 1182 (China) and at 1102, 1104 and 1179 cm−1 (Czech) to the ν3 (PO4)3− and ν3 (PO3) antisymmetric stretching vibrations. Raman bands and shoulders at 634, 613 and 579 cm−1 (China) and 611 and 596 cm−1 (Czech) are attributed to the ν4 (δ) (PO4)3− bending vibrations and those at 507, 494 and 464 cm−1 (China) and 505 and 464 cm−1 (Czech) to the ν2 (δ) (PO4)3− bending vibrations. The Raman spectrum of the OH stretching region is complex. Raman bands and shoulders are identified at 2824, 3121, 3249, 3372, 3479 and 3602 cm−1 for plumbogummite from China, and at 3077, 3227, 3362, 3480, 3518 and 3601 cm−1 for the Czech Republic sample. These bands are assigned to the ν OH stretching modes of water molecules and hydrogen ions. Approximate O–H⋯O hydrogen bond lengths inferred from the Raman spectra vary in the range >3.2–2.62 Å (China) and >3.2–2.67 Å (Czech). The minority presence of some carbonate ions in the plumbogummite (China sample) is connected with distinctive intensity increasing of the Raman band at 1106 cm−1, in which may participate the ν1 (CO3)2− symmetric stretching vibration overlapped with phosphate stretching vibrations.

The ancient gene C12orf29 : an exploration of its role in the chordate body plan

The sheep (Ovis aries) is commonly used as a large animal model in skeletal research. Although the sheep genome has been sequenced there are still only a limited number of annotated mRNA sequences in public databases. A complementary DNA (cDNA) library was constructed to provide a generic resource for further exploration of genes that are actively expressed in bone cells in sheep. It was anticipated that the cDNA library would provide molecular tools for further research into the process of fracture repair and bone homeostasis, and add to the existing body of knowledge. One of the hallmarks of cDNA libraries has been the identification of novel genes and in this library the full open reading frame of the gene C12orf29 was cloned and characterised. This gene codes for a protein of unknown function with a molecular weight of 37 kDa. A literature search showed that no previous studies had been conducted into the biological role of C12orf29, except for some bioinformatics studies that suggested a possible link with cancer. Phylogenetic analyses revealed that C12orf29 had an ancient pedigree with a homologous gene found in some bacterial taxa. This implied that the gene was present in the last common eukaryotic ancestor, thought to have existed more than 2 billion years ago. This notion was further supported by the fact that the gene is found in taxa belonging to the two major eukaryotic branches, bikonts and unikonts. In the bikont supergroup a C12orf29-like gene was found in the single celled protist Naegleria gruberi, whereas in the unikont supergroup, encompassing the metazoa, the gene is universal to all chordate and, therefore, vertebrate species. It appears to have been lost to the majority of cnidaria and protostomes taxa; however, C12orf29-like genes have been found in the cnidarian freshwater hydra and the protostome Pacific oyster. The experimental data indicate that C12orf29 has a structural role in skeletal development and tissue homeostasis, whereas in silico analysis of the human C12orf29 promoter region suggests that its expression is potentially under the control of the NOTCH, WNT and TGF- developmental pathways, as well SOX9 and BAPX1; pathways that are all heavily involved in skeletogenesis. Taken together, this investigation provides strong evidence that C12orf29 has a very important role in the chordate body plan, in early skeletal development, cartilage homeostasis, and also a possible link with spina bifida in humans.

Raman and infrared spectroscopic study of the mineral goyazite SrAl3(PO4)2(OH)5·H2O

We have studied the mineral goyazite using Raman and infrared spectroscopy. Goyazite is a member of the crandallite subgroup of the alunite supergroup. The crystal structure is of the alunite-type and consists of sheets of corner-sharing AlO6 octahedra parallel to (0001). The octahedrally coordinated Sr2+ cations occupy cavities between pairs of octahedral sheets and are surrounded by six oxygen atoms from the (Al3+)O6 octahedra. The very intense sharp band at 983 cm-1 is assigned to the ν1 PO43- symmetric stretching mode. The observation of a single band supports the concept that all the phosphate units are equivalent in the structure of goyazite. Raman bands observed at 1029 cm-1 and 1037 cm-1 are assigned to the to the ν3 PO43- antisymmetric stretching vibrations. Two Raman bands at 895 and 927 cm-1 are attributed to the stretching vibrations of H2PO4; thus indicating some hydrogen phosphate units in the structure of goyazite. Raman bands at 556, 581, 596 and 612 cm-1 are assigned to the ν4 PO43- bending modes, suggesting a reduction of symmetry of phosphate units. Two sharp Raman bands at 3609 and 3631 cm-1 are attributed to OH stretching vibrations from the goyazite hydroxyl units. Broad Raman bands at 2924, 3043, 3210, 3429 and 3511 cm-1 are assigned to water stretching vibrations. Vibrational spectroscopy enables subtle details of the molecular structure of goyazite to be determined.

Vibrational spectroscopic study of the natural layered double hydroxide manasseite now defined as hydrotalcite-2H – Mg6Al2(OH)16[CO3]⋅4H2O

Raman and thermo-Raman spectroscopy have been applied to study the mineral formerly known as manasseite now simply renamed as hydrotalcite-2H Mg6Al2(OH)16[CO3]⋅4H2O. The mineral is a member of the homonymous hydrotalcite supergroup. Hydrogen bond distances calculated using a Libowitzky-type empirical function varied between 2.61 and 3.00 Å. Stronger hydrogen bonds were formed by water units as compared to the hydroxyl units. Raman spectroscopy enabled the identification of bands attributed to the hydroxyl units. Two Raman bands at 1059 and 1064 cm-1 are assigned to symmetric stretching modes of the carbonate anion. Thermal treatment shifts these bands to higher wavenumbers indicating a change in the strength of the carbonate bonding.