Secondary Apatite Research Articles

Analysis of the Multiwalled Carbon Nanotubes Reinforced Polymethyl Methacrylate Bone Cement’s Characteristics and In Vitro Bioactivity to Prolong Its Functionality in Orthopedic Application

Polymethyl methacrylate (PMMA) bone cement is being used to fill voids that are created due to vertebral compression fractures. It is also a grouting medium in orthopedic joint replacement surgeries as they possess fast primary fixation to the bone. Considering the cement properties and in vitro bioactivity of bone cement is essential for cemented hip and knee joint replacement surgeries. In this study, commercial Simplex P bone cement (SPBC) is modified with carboxyl- (-COOH-) functionalized multiwalled carbon nanotubes (MWCNTs) to overcome high polymerization temperature, volumetric shrinkage, surface wettability, and in vitro bioactivity. A geometric dilution method is used to incorporate MWCNTs with the PMMA powder, which is in unequal proportions. The PMMA/MWCNT nanocomposite with different concentrations of reinforcements, such as 0.1, 0.3, 0.5, and 0.7 weight percentages, is prepared for the investigation. It was observed that the MWCNTs had a beneficial impact on PMMA bone cement (PMMA-BC) by enhancing its setting time (2.94%↑) and surface wettability (23.58%↑). Also, diminished polymerization temperature (29%↓) and volumetric shrinkage (40.9%↓) are observed for an optimum concentration of 0.7 wt. %. The bioactivity of the cement surface is validated by the in vitro bioactivity observed in simulated body fluid (SBF) through the development of primary and secondary apatite. It is concluded that the synthesized PMMA/MWCNT nanocomposites are found to have enhanced cement properties compared to PMMA-BC.

Composition and Formation Conditions of Neoproterozoic Phosphorites of the Middle Urals

Phosphorite breccias compose a 6-m member in the Vendian terrigenous Kernos Formation in the basin of the Mezhevaya Utka and Sylvitsa rivers in the Middle Urals. Phosphorite pebbles and gravel are accumulations of fragments of redeposited crusts, originally formed in the early diagenesis near the surface of sandy-argillaceous deposits below the water-sediment boundary. Phosphorite is represented by fluorocarbonate apatite with unit cell parameter a from 0.9359 to 0.9363 nm, spectral mode parameters in Raman spectra (FWHM = 1–2 cm–1 and position from 963 to 966 cm–1), and a band at 1095 cm–1 in IR spectra. The absorption bands at ~1430 and 1453 cm–1 in the IR spectra correspond to the substitution of the orthophosphorus group by the carbonate ion (B-type). According to thermal analysis data, the CO2 content in apatite varies in the range of 0.04–0.8%, and the admixture of dispersed organic matter in the form of aliphatic compounds is 0.3–0.8%. Apatite is represented by two generations: primary in the form of basal structureless fine-crystalline cement and secondary in the composition of euhedral crystals up to 10 µm in size. Both generations corrode detrital quartz grains. Secondary apatite is enriched in P2O5, CaO, and F and contains less SiO2, FeO, Al2O3, MgO, and K2O than primary apatite. The PAAS-normalized REE distribution has a smoothed profile with a La/Yb ratio of about 2 and positive Ce- and Eu anomalies in enrichment phosphorites. The average value of F/P2O5 is 0.09 and corresponds to that in typical fluorocarbonate apatites that have undergone catagenesis. The high values of 87Sr/86Sr (from 0.7130 to 0.7253) in detrital phosphorites of the Kernos Formation suggest their deposition in a desalinated wave-dominated shallow-marine paleobasin near a significant inflow of continental waters or catagenetic recrystallization.

Experimental study of apatite-fluid interaction and partitioning of rare earth elements at 150 and 250 °C

Abstract Apatite is a common accessory phase in igneous and metamorphic rocks. Its stability in magmatichydrothermal and hydrothermal systems is known to be a key control on the mobility of rare earth elements (REE). To better constrain how apatite is altered during fluid-rock interaction at comparably low temperatures, batch-type apatite dissolution experiments were conducted at 150 and 250 °C at saturated water vapor pressure in acidic to mildly acidic (pH of 2–4) aqueous fluids having variable salinities (0, 0.5, and 5 wt% NaCl). The study reveals the dominance of apatite dissolution textures with the formation of micrometer-scale etch pits and dissolution channels developing prominently along the c-axis of the apatite crystals. Backscattered electron imaging shows an increase in apatite dissolution with increasing temperature and upon reacting the crystals with more acidic and higher salinity starting fluids. This study also demonstrates an increase in dissolved REE in the experimental fluids corroborating with the observed apatite dissolution behavior. Backscattered electron imaging of secondary minerals formed during apatite dissolution and scanning electron microscopy-based energy dispersive spectrometry peaks for Ca, P, and REE support the formation of monazite-(Ce) and minor secondary apatite as deduced from fluid chemistry (i.e., dissolved P and REE concentrations). The studied apatite reaction textures and chemistry of the reacted fluids both indicate that the mobility of REE is controlled by the dissolution of apatite coupled with precipitation of monazite-(Ce), which are enhanced by the addition of NaCl in the starting fluids. This coupled process can be traced by comparing the REE to P ratios in the reacted fluids with the stoichiometry of the unreacted apatite crystals. Apatite metasomatized at temperatures <300 °C is therefore controlled by dissolution rather than dissolution-reprecipitation reactions commonly observed in previous experiments conducted above 300 °C. Furthermore, this study demonstrates that the presence of NaCl plays a crucial role in increasing the solubility of apatite, which controls the availability of REE to form secondary phosphates even in mildly acidic aqueous fluids. This implies that both the effects of acidity/alkalinity of the fluids and the role of dissolved alkalis (NaCl and KCl), need to be considered for understanding the controls on REE in magmatic-hydrothermal systems. Lastly, the experiments of this study expand the known conditions at which apatite is susceptible to be overprinted by hydrothermal alteration from 900 °C down to 150 °C and highlights the necessity of appropriately screening apatite grains using backscattered electron and cathodoluminescence imaging for signs of hydrothermal alteration textures in igneous apatite.

Use of high-U hydrothermal apatite containing excess 206Pb to constrain the age of uranium mineralization at the Coles Hill deposit, Virginia, USA

High-U hydrothermal apatite with complex UPb systematics is closely spatially associated with mineralization at the Coles Hill deposit, the largest unmined uranium deposit known in the United States. The deposit is hosted in metasomatized rocks of the 450- to 430-Ma-old Martinsville Intrusive Complex in south-central Virginia. Direct dating of metamict uranium-ore minerals, mostly coffinite, is not possible due to open-system radon loss. Instead, UPb isotopes in cogenetic apatite were investigated as a means of evaluating the age of mineralization. Here we report in situ electron probe microanalyses (EPMA) of coffinite, isotope-dilution thermal-ionization mass spectrometry (ID-TIMS) UPb data for mineralized whole rock samples, and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) UPb isotope data for apatite in both unmineralized and U-mineralized host rocks.Massive deficits in radiogenic Pb preclude reliable UPb “chemical ages” calculated from EPMA data obtained from coffinite. In contrast, LA-ICPMS data for secondary apatite in unmineralized rocks indicate low-U concentrations (100–102 ppm), “normal” (consistent with models of terrestrial Pb isotopic evolution) initial Pb isotope compositions, and UPb age estimates of ~330 Ma, which is consistent with dates previously proposed for the regional Paleozoic shear zone that hosts the deposit. Ore-stage apatite associated with coffinite has high-U concentrations (typically 102–103 ppm but up to 2.4 wt% U) and large excesses of 206Pb (207Pb/206Pb < 0.01) unsupported by in situ U decay. Data show that initial Pb had variable isotopic compositions including both “normal” Pb derived from host rocks and 206Pb-enriched Pb introduced by secondary metasomatic fluids. Evaluation of the complex evolution and mixing of Pb sources has broader implications for UPb dating of hydrothermal apatite.Excess 206Pb in apatite is derived from decay products of 222Rn lost from coffinite and mobilized by Na-, P-, and U-enriched metasomatic fluids during the main mineralizing event at ~230 Ma. Ore-stage alteration did not uniformly reset the UPb systematics in host rocks precluding a well-constrained whole-rock isochron age. However, whole-rock isotope data imply U mobility at ~200–220 Ma and support a Triassic age for the final stages of mineralization. Results also indicate that apatite with up to several weight percent uranium is able to retain U and its decay products for hundreds of millions of years; an important consideration when assessing this mineral as a potential matrix for long-term storage of radioactive waste.

DISCOVERY OF NEW KIMBERLITE FIELDS ON THE SOUTHERN SLOPE OF THE LEONE-LIBERIAN SHIELD (Sierra Leone)

During 2017–2018 not far from Sewafeh town, Kono province (Republic of Sierra Leone), we identified a number of previously unknown manifestations of kimberlite magmatism in the form of a system of individual veins localized at the contact of the migmatite basement and Archean ultrabasic massifs, or in the immediate vicinity of ultramafic massifs, which is part of the rocks of the greenstone belt. The optimal sequence of conducting remote sensing studies, such as interpretation of space images of various resolution, neotectonic and geomorphological analysis, SRTM modeling, and then field geological and geophysical research have facilitated this discovery. According to drilling data, kimberlites in different spots of their occurrence (Punduru 1 area) are represented by subvolcanic phlogopite-olivine (with perovskite), and olivine varieties, as well as veins of numerous intensely metasomatic altered kimberlite breccias (Yomby area). Veins of subvolcanic kimberlites are concentrated in the contact part with ultramafic massifs of magmatic and lava (metakomatiite xenoliths) genesis. Kimberlites are the youngest vein formations in the area, crossing even vein pegmatites, the generation of which was provoked by the intrusion of ultramafic rocks in the basement migmatites (Cederholm effect). Kimberlites are present in the section of wells in the form of separate veins of complex morphology and thickness from a few centimeters to 45 cm. In well P1-2 at a depth of 92 m, these are represented by micro porphyry kimberlites of the basaltoid type with microlithic groundmass, altered by secondary metasomatic processes. Porphyry inclusions are represented by pseudomorphs of carbonate-serpentine composition after olivine and rare phlogopite flakes. Olivine crystals of the second-generation act as micro porphyry inclusions. The rock matrix is carbonate. Carbonate is represented by finely crystalline calcite, or replaced by dolomite. In addition to olivine, the groundmass contains relics or pseudomorphs after phlogopite, as well as magnetite, perovskite (it can be replaced by magnetite), secondary apatite. The kimberlites of the Bambawo area are represented by sub-volcanic porphyry basaltoid kimberlites, autolithic kimberlites and kimberlite xenotuff breccias.

Nanoscale constraints on a fluid-induced transformation of monazite during postmagmatic alteration – A case of the Jawornik granitoid (NE Orlica-Śnieżnik Dome, Sudetes, SW Poland)

Two monazite grains altered during postmagmatic, hydrothermal processes in the Variscan Jawornik granitoid (NE Orlica-Śnieżnik Dome, Sudetes, SW Poland) were investigated. Different assemblages of secondary phases replacing and forming close to altered monazite indicate two different courses of the mineral-fluid reactions. The first monazite is surrounded by two zones comprising rhabdophane group minerals (rhabdophane henceforth) and hematite (inner zone) and allanite (outer zone) that form a concentric corona texture. The growth of secondary phases is interpreted as being related to decreasing temperatures below ca. 500 °C. The inner zone formed due to alteration of the monazite that was driven by fluid-induced coupled dissolution-reprecipitation reactions. This alteration resulted in the progression of partial replacement by submicron layers of rhabdophane along the monazite surface and pseudomorphic replacement of a substantial part of the monazite by rhabdophane and hematite. The presence of the hematite suggests oxygen fugacity above the hematite-magnetite buffer. Alteration of the second investigated monazite is related to dissolution induced by a K-bearing alkali fluid, partial replacement by thorianite (ThO2), and overgrowth by K-feldspar with minor titanite formed during the chloritization of biotite and the alteration of feldspars. These results demonstrate that the local character of mineral-fluid reactions can take an entirely different course at the microscale, within a distance of several hundreds of microns. The assemblages of secondary phases replacing two investigated monazite grains indicate that the alteration processes are related to moderate temperature (<500 °C) hydrothermal processes assigned to upper greenschist facies conditions. The absence of secondary apatite (close to the first monazite) and secondary REE- and P-bearing phases (close to the second monazite) indicates the high mobility of the elements removed by the fluid, in contrast to the low mobility of the Th taken up by secondary rhabdophane or thorianite crystallizing at the monazite surface. The presence of rhabdophane group minerals and thorianite in hydrothermal secondary phases assemblages replacing monazite can be used as indicators of the local character of the environment at the microscale.

Assessing bone transformation in late Miocene and Plio‐Pleistocene deposits of Kenya and South Africa

Bone reactivity offers a potential way to record local physical–chemical conditions prevailing in fossilization environments and archaeological sites. In the present study, a series of fossil bone samples from the karstic environments of the Bolt's Farm cave system (Cradle of Humankind, South Africa) and from fluvio‐lacustrine environments of the Tugen Hills (Gregory Rift, Kenya) is analysed. The chemical composition and infrared and nuclear magnetic resonance (NMR) spectroscopic properties of fossil samples point to a transformation of the biogenic apatite and formation of secondary apatite. Depending on the sample, the secondary apatite corresponds to a carbonate‐bearing hydroxy‐ or fluor‐apatite. The maximum fraction of secondary apatite is close to 60%, coinciding with previous observations in experimental alteration of bone in aqueous solutions and suggesting that a fraction of pristine biological apatite is likely to be preserved. The present results also suggest that the acetic acid treatment of fossil samples moderately increases their average crystallinity but may dissolve carbonate‐rich domains of secondary apatite.

Atomic scale transformation of bone in controlled aqueous alteration experiments

The chemical and isotopic compositions of biogenic apatite are important geochemical markers, which can suffer modifications during fossilisation. Compared with modern ones, fossil apatites generally exhibit variations in carbonate content, enrichment in fluorine, incorporation of trace elements and an increase in crystallinity parameters. Detailed understanding of these transformations induced by fossilisation should help assess the preservation of geochemical records in apatites. In this contribution, we investigate the transformation of modern bone altered under controlled conditions. Modern bone samples were soaked in aqueous solutions of neutral to alkaline pH (9–10) for one and three weeks at various temperatures (20 and 70 °C) and experiments were duplicated in fluorine-free and in 10−2 M NaF solutions. Bone transformation was monitored through the modifications of chemical (F, Ca, P) and isotopic (δ13C, δ18Oc, δ18Op) composition as well as using vibrational (ATR-FTIR, Raman) and solid-state (1H, 13C, 19F) NMR spectroscopies. The observed modifications sustain a transformation mechanism through partial dissolution of biogenic apatite and precipitation of secondary apatite. This transformation occurs irrespective of the presence or absence of fluorine and leads to the formation of carbonate-bearing fluorapatite or carbonate-bearing hydroxylapatite, respectively. The fraction of secondary apatite seems to be limited to ~60%, suggesting that its formation has a protecting role against further dissolution of the primary apatite. The observation of clumped (CO32−, F−) defects in the structural B-site of some samples as well as perturbation of the isotopic compositions attest to carbonate incorporation in the secondary apatite. Although the incorporation of fluoride ions can serve as a probe revealing dissolution-recrystallization of bone, the present study also underlines the difficulty to systematically relate mineralogical transformations to an open-system behaviour in bioapatite.

Fabrication and in vitro properties of zinc-based superhydrophilic bioceramic coatings on zirconium

In this study, as the first step, the bioceramic coatings were fabricated on Zr (commercial pure zirconium) in calcium acetate and β‑calcium glycerophosphate salt-based electrolyte by MAO (micro arc oxidation). And then, as the second step, the Zn (zinc) thin film layer measured an average thickness of 5 nm was coated on the MAO surface by TE (thermal evaporation). The phase composition, surface and cross sectional morphology, elemental composition and wettability of the MAO and Zn-based MAO coatings were analyzed by powder-XRD and TF-XRD, SEM, EDS-mapping and contact angle goniometer, respectively. The phases of cubic-ZrO2, perovskite-CaZrO3 and HA (hydroxyapatite) were observed on the surfaces by powder and TF-XRD analyses. The morphology of the MAO surface was not changed by TE although the chemistry of it was different from the MAO surface. The surfaces of both coatings were porous and rough. The Zn was uniformly deposited through the whole surface. After TE process, the wettability of the surface decreased and the Zn-based surface exhibited superhydrophilicity compared to MAO surface. In vitro bioactivity test of both coatings were investigated by immersion test in SBF (simulated body fluid) up to 10 days. The bone like apatite layer (secondary apatite) on the Zn-based bioceramic surface was compact and uniform compared the one on the MAO surface although it was completely propagated through both surfaces. In vitro anti-bacterial test of both coatings were carried out by microbial adhesion for Gram positive and Gram negative bacteria. It was observed that the microbial adhesions of the Zn-based bioceramic surfaces were lower than ones of the MAO bioceramic surfaces for all Gram-positive and Gram-negative bacteria.

In vitro properties of bioceramic coatings produced on zirconium by plasma electrolytic oxidation

The bioceramic coatings were formed on zirconium (Zr) at different treatment times such as 5, 10 and 15min in a calcium acetate and β-calcium glycerophosphate-based electrolyte by a single-step plasma electrolytic oxidation (PEO). The XRD and FTIR confirmed a presence of highly crystalline cubic-ZrO2, perovskite-CaZrO3 and HAP on the surface of Zr. The surface of the coatings was porous and rough due to the existence of micro-sparks through the PEO process. The surface of the coatings produced at long treatment times exhibited a hydrophilic surface compared to the uncoated Zr substrate. The elements of Ca, P and O were homogeneously distributed through on the coated surface. The amount of secondary apatite formed on coated surface after immersion in simulated body fluid (SBF) up to 28days increased with increasing time. The bioactivity of the coatings was greater than that of the uncoated Zr. The bacterial adhesion to the coated surface decreased considerably compared to the uncoated Zr. MTT analysis showed that a cell viability, a cell attachment and a cell growth for PEO coatings were greater than for the uncoated Zr. As a result, the biological test results show that PEO coatings with different treatment time improve the biocompatibility of the surfaces.

Diagenesis does not invent anything new: Precise replication of conodont structures by secondary apatite

Conodont elements are important archives of sea/pore water chemistry yet they often exhibit evidence of diagenetic mineral overgrowth which may be biasing measurents. We decided to investigate this phenomenon by characterising chemically and crystallographically, the original biomineral tissue and the diagenetic mineral nature of conodont elements from the Ordovician of Normandy. Diagenetic apatite crystals observed on the surface of conodont elements show distinctive large columnar, blocky or web-like microtextures. We demonstrate that these apatite neo-crystals exhibit the same chemical composition as the original fossil structure. X-ray microdiffraction has been applied herein for the first time to conodont structural investigation. Analyses of the entire conodont element surface of a variety of species have revealed the existence of a clear pattern of crystal preferred orientation. No significant difference in unit cell parameters was documented between the newly formed apatite crystals and those of the smooth conodont surfaces, thus it emerges from our research that diagenesis has strictly replicated the unit cell signature of the older crystals.

Sensitive high-resolution ion microprobe U-Pb dating of baddeleyite and zircon from a monzonite porphyry in the Xiaoshan area, western Henan Province, China: Constraints on baddeleyite and zircon formation process

Baddeleyite and zircon, including zircon overgrowths on baddeleyite, co-occur in a granophyric monzonite porphyry intruding volcanic rocks of the Majiahe Formation of the Xiong’er Group in the Xiaoshan area of the western Henan Province (China). It is inferred that the low silica content of the initial magma resulted in the formation of euhedral baddeleyite. Sensitive high-reso­lution ion microprobe (SHRIMP) U-Pb dating of the baddeleyite yields a weighted mean 207 Pb/ 206 Pb age of 1779 ± 8 Ma, representing the crystallization of the porphyry. Survival of baddeleyite as the magma became silica saturated implies a rapid cooling process. Zircon grains in the porphyry are anhedral to needle shaped, and are often clustered together within K-feldspar stringers or along the interface of quartz and K-feldspar in the granophyric groundmass, suggesting undercooling likely due to rapid emplacement. These observations indicate that zircon did not crystallize until final emplacement. Our U-Pb analyses of zircon yield a weighed mean 207 Pb/ 206 Pb age of 1777 ± 8 Ma, similar to that of baddeleyite. Subsequent medium- to high-temperature hydrothermal alteration affected most minerals at subsolidus conditions. Amphibole-plagioclase thermobarometry indicates pressure of 2.4–4.3 kbar and temperature of 470–580 °C for this alteration stage. Related alteration, such as total albitization of plagioclase, crystallization of secondary apatite, and sporadic secondary zircon overgrowths on baddeleyite, indicates that the fluid phase was enriched in Si, Na, and halogens (e.g., F, Cl). In addition to direct replacement of baddeleyite, zirconium required for the development of zircon overgrowths may also have been available through the alteration of Zr-bearing matrix phases such as amphibole and ilmenite.

Neoproterozoic (ca. 820–830 Ma) mafic dykes at Olympic Dam, South Australia: Links with the Gairdner Large Igneous Province

A suite of basaltic to doleritic dykes (named the Olympic Dam dolerite) has been intersected in drill holes at the Olympic Dam iron oxide Cu–U–Au–Ag deposit in the Gawler Craton, South Australia. The dykes intrude the ca. 1600Ma Roxby Downs Granite as well as the Olympic Dam Breccia Complex, and range from several centimetres to over 100m in width, strike NW and dip subvertically. Clinopyroxene and plagioclase are the major minerals, together with accessory apatite and Ti-magnetite. Magmatic apatite crystals in medium-grained doleritic dykes have been dated by LA-ICPMS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry), and yielded a U–Pb age of 825±18Ma. The Olympic Dam dolerite has invariably been altered. Secondary apatite and titanite crystals from post-magmatic veinlets cutting the same dykes give similar results of 821±15Ma and 817±11Ma, respectively. All these results are, within error, coincident in age with the Gairdner Dyke Swarm, the longest dyke swarm (∼1000km in length) in Australia. The Olympic Dam dolerite shows similar compositional trends and variations to the Gairdner Dyke Swarm, especially in terms of the relatively immobile High Field Strength Elements (HFSE) and Rare Earth Element (REE). We conclude that the Olympic Dam dolerite belongs to the Gairdner Dyke Swarm, expanding its known extent and compositional range. The Gairdner Dyke Swarm is a major component of the ca. 820Ma Gairdner Large Igneous Province (LIP) generated during the break-up of the supercontinent Rodinia. The ca. 1070Ma Warakurna and the ca. 820Ma Gairdner LIP in Australia are compositionally distinct, whereas the Gairdner LIP and LIP and mafic suites associated with the break-up of Rodinia in South China and North America are broadly similar. This provides geochemical support for a Gairdner LIP origin for some mafic suites, in particular the Beda Volcanics in South Australia, and for a juxtaposition of South China, South Australia and North America in the tectonic reconstruction of Rodinia at ca. 820Ma.

Bioactive coatings on Ti6Al4V alloy formed by plasma electrolytic oxidation

Abstract In this study, coatings, consisting of hydroxyapatite and titanium oxide bioceramic phases, were produced on Ti6Al4V alloy by plasma electrolytic oxidation for different times in a solution containing calcium acetate and β-calcium glycerophosphate. The phases of anatase, rutile, TCP (Ca3(PO4)2), perovskite-CaTiO3 and hydroxyapatite (HAp, Ca10(PO4)6(OH)2) were detected in the PEO coatings. The crystallinity of these phases was enhanced with increasing treatment time. The friction and wear resistance properties of the PEO coatings in simulated body fluid (SBF) were substantially improved compared to Ti6Al4V alloy. The corrosion resistance of the PEO samples in SBF was determined by an electrochemical method, and found to be significantly improved compared to Ti6Al4V alloy due to the existence of titanium oxide and the calcium phosphate-based phases. The amount of apatite induced at the PEO surface increased with increasing immersion time in SBF at 36.5 °C. According to the SEM images and FTIR results, after soaking in SBF for 14 days, the amount of secondary apatite formed in the coating electrolytically oxidized for 90 min was maximized due to high surface area and high amount of TiO2 and HAp in the coating structure.

Origin and paleoenvironmental interpretation of aluminum phosphate–sulfate minerals in a Neoproterozoic Baltic paleosol

Aluminum phosphate–sulfate (APS) mineral solid-solutions occur as accessory phases in different sedimentary and hydrothermal deposits. Their composition is a sensitive environmental indicator recording changes in pH, temperature and chemical composition of the weathering, diagenetic or hydrothermal fluids. In this contribution we studied APS mineralization in a Neoproterozoic paleotropical paleosol developed on Paleo–Mesoproterozoic crystalline basement in the Baltic Basin. Small and disseminated APS minerals occur in high abundance (up to 4wt.% of crystalline phases) in the weathering profile developed on gabbroic rocks rich in magmatic apatite. APS minerals belonging to a goyazite–florencite–svanbergite–woodhouseite solid-solution series occur in the uppermost part of the weathering profile and are replaced down-profile with secondary apatite. The change from APS minerals to secondary apatite precipitates reflects a paleo-pH gradient in the weathering profile from acidic (pH<6) in the uppermost few meters in the APS precipitation zone, to neutral or near neutral at 4–5m-depth from the paleoweathered surface where secondary apatite occurs. Typically uniform <5μm-size APS crystallites suggest rapid precipitation in a highly supersaturated solution, but these crystals show a fine zonal structure whose nature and formation mechanism remain unclear.

Acrylic cement formulations modified with calcium deficient apatite nanoparticles for orthopaedic applications

Polymethyl methacrylate-based bone cements are used worldwide by the orthopaedic surgeons to secure joint implants with the skeleton. However, the clinical use of this cement is accompanied by complications such as exothermic heat produced during the polymerization reaction, lack of bone bonding ability and shrinkage to name a few. In the present work, the effect of incorporation of calcium-deficient hydroxyapatite nanoparticles on the properties of a commercially available orthopaedic bone cement matrix has been investigated. Initial and final setting time of the cement has been found to decrease with calcium-deficient hydroxyapatite nanoparticles addition. The exothermic heat dissipation during the polymerization has been found to significantly decrease with the calcium-deficient hydroxyapatite nanoparticle incorporation in the bone cement. Contact angle study revealed that with the increasing percentage of calcium-deficient hydroxyapatite nanoparticle, the composite cement becomes more hydrophilic. In vitro biomineralization study confirmed the bioactivity of the nanocomposite bone cement with the formation of primary and secondary apatite on the cement surface. Present study suggests that the incorporation of calcium-deficient hydroxyapatite nanoparticle into the orthopaedic bone cements could help to overcome some of the shortcomings of the orthopaedic cement.

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) A, b = 12.7314(16) A, c = 11.980(4) A, β = 108.38(4) , V = 1396.2(8) A3, 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 e-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.

Soil–geomorphology interactions and paleoclimatic implications of an ornithogenic soil toposequence on Rata Island, Fernando de Noronha Archipelago, South Atlantic

The formation of highly phosphatized soils on sites of avian activity is a common feature of oceanic islands. We characterized a toposequence of phosphatic soils on Rata Island, to evaluate the soil genesis based on local topographic variations. For this purpose, four soils ranging from the upper hill down to the lowest landscape position on the island, representing a range of parent materials (basalt and calcareous sands), were analyzed. In the lowest landscape position a shallow Regosol was identified, strongly influenced by birds and marine sprays, developed on “karstified” Pleistocene calcarenites; the three other soils in the upper part of the toposequence are Ornithogenic Cambisols, ranging from a deep Cambisol profile on Basalt lava to intermediate Cambisols on mixed colluvial sediments of the basalt/calcareous. The lowermost Regosol is associated with a rugged landscape with strong calcarenite dissolution and karstification. The soil phosphatization is clearly an inherited process of the Late Quaternary age, when climate conditions were different. Initial weathering took place in the last interglacial period, under wetter conditions during which the Tertiary basalts were strongly weathered, leaving corestones in a saprolitic, oxidized mass. In the late Pleistocene, a gentle surface distributed these weathering products along the pediment slopes as colluvial materials, whereas in the coastal areas aeolian processes formed large sand dunes composed of reworked calcareous sands from marine sources during a time of very low sea level. During this time, widespread bird activity accounted for secondary apatite formation on the surface of calcareous oolites. Finally, the Holocene warming was accompanied by increasing sea level, enhanced tropical weathering, Fe and Al mobility and variscite formation superimposed on degraded Ca-phosphates, forming two phase phosphatic aggregates.

Petrography and Mineral Chemistry of Alkaline–Carbonatite Complex in Singhbhum Crustal Province, Purulia Region, Eastern India

Abstract: The variant rock types of an Alkaline–Carbonatite Complex (ACC) comprising alkali pyroxenite, nepheline syenite, phoscorite, carbonatite, syenitic fenite and glimmerite along with REE and Nb–mineralization are found at different centres along WNW-ESE trending South Purulia Shear Zone (SPSZ) in parts of Singhbhum Crustal Province. The ACC occurs as intrusions within the Mesoproterozoic Singhbhum Group of rocks. Alkali pyroxenite comprises of aegirine augite, magnesiotaramite, magnesiokatophorite as major constituents. Pyrochlore and eucolite are ubiquitous in nepheline syenite. Phoscorite contains fluorapatite, dahllite, collophane, magnetite, hematite, goethite, phlogopite, calcite, sphene, monazite, pyrochlore, chlorite and quartz. Coarse fluorapatite shows overgrowth of secondary apatite (dahllite). Secondary apatite is derived from primary fluorapatite by solution and reprecipitation. The primary fluorapatite released REE to crystallize monazite grains girdling around primary apatite. Carbonatite is composed dominantly of Srcalcite along with dolomite, tetraferriphlogopite, phlogopitic biotite, aegirine augite, richterite, fluorapatite, altered magnetite, sphene and monazite. The minerals comprising of the carbonatite indicate middle stage of carbonatite development. Fenite is mineralogically syenite. Glimmerite contains 50–60% tetraferriphlogopite. An alkali trend in the evolution of amphiboles (magnesiotaramite–magnesiokatophorite–richterite) and chinopyroxenes (aegirine augite, aegirine) during the crystallization of the suite of rocks is noted. Monazite is the source of REE in phoscorite and carbonatite. Fluorapatite has low contents of REE, PbO, ThO2 and UO2. Pyrochlore reflects Nb-mineralization in nepheline syenite and it is enriched in Na2O, CaO, TiO2, PbO and UO2. Pyrochlore containing UO2 (6.605%) and PbO (0.914%) in nepheline syenite has been chemically dated at 948 ± 24 Ma by EPMA.

Timing of hydrothermal activity associated with the Douzhashan uranium-bearing granite and its significance for uranium mineralization in northeastern Guangxi, China

The Miaoershan uranium (U) ore field in northeastern Guangxi is one of the important granite-related U deposits in south China and is closely related to the Douzhashan U-bearing granite. The Douzhashan granite contains primary U-rich accessory minerals, including monazite (UO2 = 0.98–1.75 wt%) and xenotime (UO2 = 1.48–6.14 wt%). Primary monazite and xenotime yield chemical ages of 231 ± 28 Ma and 230 ± 38 Ma by electron microprobe analysis and U-Pb isotopic ages of 220±6 Ma and 211±7 Ma by laser ablation-inductively coupled-mass spectrometry respectively. These ages demonstrate that the Douzhashan granite formed during the period of Indosinian magmatic activity. Back scattered electron imaging shows that monazite and xenotime are commonly altered to assemblages of low-U synchisite and apatite, which was associated with loss of U to hydrothermal fluids. U-Th-Pb analyses of secondary apatite yielded a chemical age of 136 ± 17 Ma, which corresponds to the timing of Cretaceous-Tertiary crustal extension in south China. We suggest that the heat and CO2 required for mineralization was the result of Yanshanian crustal extension, and that this triggered the breakdown of U-rich accessory minerals in the Douzhashan U-bearing granite. Uranium remobilization from the Douzhashan granite provided materials for mineralization within the granite and/or surrounding country rocks. Therefore, a combination of Indosinian compression and Yanshanian extensional overprint produced the hydrothermal U deposits associated with the Douzhashan granite.