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A major debris flow, the Trig Point Hill flow, originating from Kerimasi volcano (Tanzania) contains numerous blocks of extrusive/pyroclastic carbonatites similar to those exposed at the rim of the currently inactive crater. The blocks of calcite carbonatite consist of: (1) large clasts of corroded and altered coarse grained calcite; (2) primary prismatic inclusion bearing phenocrystal calcite; and (3) a matrix consisting primarily of fine-grained prismatic calcite. The large clasts are inclusion free and exhibit a ‘corduroy-like’ texture resulting from solution along cleavage planes. The resulting voids are filled by brown Fe–Mn hydroxides/oxides and secondary calcite. The prismatic or lath-shaped phenocrystal calcite is not altered and contains melt inclusions consisting principally of primary Na–Ca carbonates which contain earlier-formed crystals of monticellite, periclase, apatite, Mn–Mg-magnetite, Mn–Fe-sphalerite and Nb-perovskite. Individual Na–Ca carbonate inclusions are of uniform composition, and the overall range of all inclusions analysed (wt.%) is from 28.7 to 35.9 CaO; 16.7–23.6 Na2O; 0.5–2.8 K2O, with minor SO3 (1.1–2.2) and SrO (0.34–1.0). The Na–Ca carbonate compositions are similar to that of shortite, although this phase is not present. The Na–Ca carbonates are considered to be primary deuteric phases and not secondary minerals formed after nyerereite. Monticellite shows limited compositional variation and contains 2–4 wt.% MnO and 12 wt.% FeO and is Mn-poor relative to monticellite in Oldoinyo Lengai natrocarbonatite. Periclase is Fe-bearing with up to 13 wt.% FeO. Spinels are Cr-free, Mn-poor and belong to the magnetite–magnesioferrite series in contrast to Mn-rich spinels of the magnetite–jacobsite series occurring in Oldoinyo Lengai natrocarbonatite. The matrix in which the ‘corduroy’ clasts and phenocrystal calcite are set consists of closely packed small prisms of calcite lacking melt inclusions, with interstitial fine-grained apatite, baryte, strontianite and minor fluorite. Pore spaces are filled with secondary Mn–Fe hydroxides/oxides, anhydrite and gypsum. The hypothesis that flow-aligned calcite in volcanic calciocarbonatites from Kerimasi, Tinderet, Homa and Catanda is altered nyerereite is discussed and it is considered that these calcite are either primary phases or altered melilite. The nyerereite alteration hypothesis is discussed with respect to the volumetric and compositional aspects of pseudomorphism by dissolution–precipitation replacement mechanisms. This study concludes that none of the volcanic calciocarbonatites containing flow-aligned calcite phenocrysts are altered natrocarbonatite.

Distinctly different groundmass mineralogy characterise the hypabyssal facies, Mesoproterozoic diamondiferous P3 and P4 intrusions from the Wajrakarur Kimberlite Field, southern India. P3 is an archetypal kimberlite with macrocrysts of olivine and phlogopite set in a groundmass dominated by phlogopite and monticellite with subordinate amounts of serpentine, spinel, perovskite, apatite, calcite and rare baddeleyite. P4 contains mega- and macrocrysts of olivine set in a groundmass dominated by clinopyroxene and phlogopite with subordinate amounts of serpentine, spinel, perovskite, apatite, and occasional gittinsite, and is mineralogically interpreted as an olivine lamproite. Three distinct populations of olivine, phlogopite and clinopyroxene are recognized based on their microtextural and compositional characteristics. The first population includes glimmerite and phlogopite–clinopyroxene nodules, and Mg-rich olivine macrocrysts (Fo 90–93) which are interpreted to be derived from disaggregated mantle xenoliths. The second population comprises macrocrysts of phlogopite and Fe-rich olivine (Fo 81–89) from P3, megacrysts and macrocrysts of Fe-rich olivine (Fo 85–87) from P4 and a rare olivine–clinopyroxene nodule from P4 which are suggested to have a genetic link with the precursor melt of the respective intrusions. The third population represents clearly magmatic minerals such as euhedral phenocrysts of Fe-rich olivine (Fo 85–90) crystallised at mantle depths, and olivine overgrowth rims formed contemporaneously with groundmass minerals at crustal levels. Close spatial association and contemporaneous emplacement of P3 kimberlite and P4 lamproite is explained by a unifying petrogenetic model which involves the interaction of a silica-poor carbonatite melt with differently metasomatised wall rocks in the lithospheric mantle. It is proposed that the metasomatised wall rock for lamproite contained abundant MARID-type and phlogopite-rich metasomatic veins, while that for kimberlite was relatively refractory in nature.

To aid development of cost-effective sintered spinel as a refractory raw material, this paper presents an extensive analysis of microstructure and complex phase evolution of Al-rich, Mg-rich, and stoichiometric spinel aggregates derived from Indian magnesite and calcined alumina. Pore morphology in Al-rich spinel was transformed upon sintering at 1650°C and corundum laths embedded in porous Al-rich spinel matrix was formed. Stoichiometric spinel sintered at 1600°C consisted of mostly direct bonded angular equiaxed spinel grains which incorporated the impurities in solid solution. Mg-rich spinel was composed of spinel grains with reduced angularity along with intergranular amorphous phase, small round monticellite grains, and periclase. EDS line scan revealed impurity-free joins existed between direct bonded spinel grains. Mg-rich spinel containing 0.65 wt% ZrO2 formed cubic ZrO2-CaO-MgO solid solution located along spinel boundaries, which reduced both intergranular amorphous phase and monticellite. This increased SiO2 and MgO content in spinel solid solution triggering exsolution of metastable cubic forsterite manifested as split spinel peaks in XRD pattern. A 14.7% reduction in slag penetration was exhibited upon doping Mg-rich spinel with 0.21% ZrO2. Stoichiometric and Mg-rich spinels attained 0.35% and 0.54% apparent porosity at 1600°C, which is better than most commercial sintered refractory spinels.

The abundance and distribution of halogens (F, Cl) are rarely recorded in kimberlites and therefore their petrogenetic significance is poorly constrained. Halogens are usually present in kimberlite rocks in the structure of phlogopite and apatite, but their original concentrations are never fully retained due to the effects of alteration. To provide new constraints on the origin and evolution of halogens in kimberlites and their melts, we present a detailed study of the petrography and geochemistry of the late-Cretaceous Group-I (or archetypal) Roger kimberlite (Ekati cluster, Canada). The studied samples contain abundant anhedral-to-euhedral olivine which is set in a crystalline groundmass of monticellite, phlogopite, apatite, spinel (i.e. magnesian ulvospinel-magnetite (MUM), Mg-magnetite, pleonaste, Cr-spinel), and perovskite along with abundant secondary alteration phases (i.e. serpentine, garnet (andradite-schlorlomite), amakinite ((Fe2 +, Mg, Mn)(OH)2), calcite). The Roger kimberlite is characterised by the highest recorded F-content (up to 2688 ppm) of the Ekati cluster kimberlites, which is reflected by the preservation of F-rich phases, where bultfonteinite (Ca4(Si2O7)(F, OH)2) and fluorite commonly replace olivine. In order to examine the composition and evolution of the kimberlite melt prior to post-magmatic processes, we studied melt inclusions in olivine, Cr-spinel, monticellite and apatite. Primary multiphase melt inclusions in Cr-spinel, monticellite and apatite and secondary inclusions in olivine are shown to contain a diversity of daughter phases and compositions that are dominated by alkali/alkali-earth (Na, K, Ba, Sr)-enriched Ca-Mg-carbonates ± F, Na-K-chlorides and sulphates, phosphates ± REE, spinel, silicates (e.g. olivine, phlogopite, (clino)humite), and sulphides. Although alkali/alkali-earth- and halogen-bearing phases are abundant in melt inclusions, they are generally absent from the kimberlite groundmass, most likely due to ubiquitous effects of syn- and/or post-magmatic alteration (i.e. serpentinisation). Comparisons between halogens and other trace elements of similar compatibility (i.e. F/Nd and Cl/U) in the Roger kimberlite and their respective estimated primitive mantle abundances show that halogens should be a more significant component in kimberlites than typically measured. We propose that fluorine in the Roger kimberlite was magmatic and was redistributed during hydrothermal alteration by Ca-bearing serpentinising fluids to produce the observed bultfonteinite/fluorite assemblages. Based the compositions and daughter mineral assemblages in primary melt inclusions and reconstructed halogen abundances, we suggest that Cr-spinel, monticellite and apatite crystallised from a variably differentiated Si-P-Cl-F-bearing carbonate melt that was enriched in alkalis/alkali-earths and highly incompatible trace elements.

The small upper Pleistocene diatreme of Polino (central Italy) is known in literature as one of the few monticellite alvikites (volcanic Ca-carbonatite) worldwide. This outcrop belongs to the Umbria-Latium Ultra-alkaline District (ULUD), an area characterized by scattered and small-volume strongly SiO2-undersaturated ultrabasic igneous rocks located in the axial sector of the Apennine Mts. in central Italy. Petrographic and mineralogical evidences indicate that Polino olivine and phlogopite are liquidus phases rather than mantle xenocrysts as instead reported in literature. The presence of monticellite as rim of olivine phenocrysts and as groundmass phase indicates its late appearance in magma chambers at shallow depths, as demonstrated by experimental studies too. The absence of plagioclase and clinopyroxene along with the extremely MgO-rich composition of olivine (Fo92–94) and phlogopite (average Mg# ~93) suggest for Polino magmas an origin from a carbonated H2O-bearing mantle source at depths at least of 90–100 km, in the magnesite stability field. In contrast with what reported in literature, the ultimate strongly ultrabasic Ca-rich whole-rock composition (~15–25 wt% SiO2, ~31–40 wt% CaO) and the abundant modal groundmass calcite are not pristine features of Polino magma. We propose that the observed mineral assemblage and whole-rock compositions result mostly from the assimilation of limestones by an ultrabasic melt at a depth of ~5 km. A reaction involving liquidus olivine + limestone producing monticellite + CO2 vapour + calcite is at the base of the origin of the Polino pseudocarbonatitic igneous rocks.

Indian magnesites from Salem and Almora regions were selected for the present study. Chemical analysis of these magnesites confirmed that Salem region magnesite (SM) contains CaO and SiO2, whereas Almora origin magnesite (AM) shows higher amount of Fe2O3 and CaO as major impurities. Crystalline phases developed in sintered Salem magnesite are periclase, forsterite and monticellite, while magnesioferrite and monticellite are found in sintered Almora magnesite apart from periclase as major phase. Microstructural analyses reveal that sintered SM has lower grain size than sintered AM . Although, no significant difference was noticed at room temperature flexural strengths of both the sintered samples, but sintered AM samples exhibit better flexural strength at elevated temperature (1200°C).

A shallow-level monzodioritic to quartz-monzodioritic pluton of the Upper Cretaceous age caused contact metamorphism of Tithonic&ndash, Kimmeridgian reef limestones at Măgureaua Vaţei (Metaliferi Massif, Apuseni Mountains, Romania). The preserved peak metamorphic assemblage includes gehlenite (Ak 33.64&ndash, 38.13), monticellite, wollastonite-2M, Ti-poor calcic garnet, and Ca-Tschermak diopside (with up to 11.15 mol.% Ca-Tschermak molecule). From the monzodioritic body to the calcitic marble, the periplutonic zoning can be described as: monzodiorite/agpaitic syenite-like inner endoskarn/wollastonite + perovskite + Ti-poor grossular + Al-rich diopside/wollastonite + Ti-poor grossular + diopside + vesuvianite/gehlenite + wollastonite + Ti poor grossular + Ti-rich grossular (outer endoskarn)/wollastonite + vesuvianite + garnet (inner exoskarn) / wollastonite + Ti-rich garnet + vesuvianite + diopside (outer exoskarn)/calcitic marble. Three generations of Ca garnets could be identified, as follows: (1) Ti-poor grossular (Grs 53.51&ndash, 81.03 mol.%) in equilibrium with gehlenite, (2) Ti-rich grossular (Grs 51.13&ndash, 53.47 mol.%, with up to 19.97 mol.% morimotoite in solid solution), and (3) titanian andradite (Grs 32.70&ndash, 45.85 mol.%), with up to 29.15 mol.% morimotoite in solid solution. An early hydrothermal stage produced retrogression of the peak paragenesis toward vesuvianite, hydroxylellestadite (or Si-substituted apatite), clinochlore, &ldquo, hibschite&rdquo, (H4O4-substituted grossular). A late hydrothermal event induced the formation of lizardite, chrysotile, dickite, thaumasite, okenite and tobermorite. A weathering paragenesis includes allophane, C-S-H gels and probably portlandite, unpreserved because of its transformation in aragonite then calcite. Overprints of these late events on the primary zoning are quite limited.

Indian magnesite mineral has substantial amount of impurities like CaO, SiO2 & Fe2O3. During sintering at elevated temperature these impurities react to form low melting phases like monticellite (CMS), which can degrade the high temperature properties of magnesite. In the present study, ZrO2 was added to reduce the formation of low melting phase in order to improve the hot strength. Amount of additive was varied between 2 and 6 wt.% with respect to raw magnesite. It was observed that addition of ZrO2 reduces the formation of low melting CMS at higher temperature and improves the flexural strength at 1200 °C. Periclase grain shape also changed from rounded to subrounded in the presence of zirconia.

Leaching of slag must be limited when slag is used in other areas than landfill. As slag is composed of different minerals, the properties of slag, inter alia the dissolution, depend on these minerals. If the leaching properties of each mineral are known, counter measurements can be taken to prevent the leaching of unwanted elements. In this study, the dissolution of three common slag minerals will be examined. The three minerals; boron-stabilised β-dicalcium silicate, pseudowollastonite and monticellite were synthesised. The dissolution was measured by setting pH to 4, 7 or 10 and adding 0.05 g mineral in the size range 20-38 mm and the HNO3 consumption required to maintain the pH level was recorded during 40 h. As expected, the dissolution increases for all minerals when pH decreases. The boron-stabilised β-dicalcium silicate was the only mineral fully dissolved at all pH levels, while pseudowollastonite and monticellite only dissolved completely at pH 4.On doit limiter le lessivage de la scorie lorsqu'...

Roman slag from the archaeological site near Mosnje (NW Slovenia) was studied with respect to its mineralogical and geochemical characteristics. Samples were analysed with light microscopy, X-ray powder diffraction (XRD), scanning electron microscopy with an energy dispersive spectrometer (SEM-EDS) and Raman microspectroscopy. A chemical investigation was carried out using inductively coupled plasma-atomic emission spectroscopy (ICP-ES) to determine the major elements. The investigated slags are recognized as iron slags, grouped into two main classes according to their chemical and mineralogical compositions. The first group is characterized by high Fe2O3 and low SiO2 contents and the second by high CaO and SiO2 and low Fe2O3 contents. The phase occurrence obviously depends on the chemical composition as the first group mainly consists of fayalite, wustite and magnetite, and the second one of augite, leucite, hedenbergite, monticellite and kirschsteinite.

This work aims at studying rate of densification, resistance to hydration and slag attack of 0.0–2.0 wt.% ilmenite-doped MgO-dolomite refractories fired at 1400–1700 °C, in relation to their thermal equilibrium and microfabric. XRF, XRD, SEM, EDAX and mercury intrusion were used to characterize the fired samples. The modular system MgO-MF(MA)-C2S-M2S was applied in determining their thermal equilibrium data. The rate of hydration and attack by steel-slag were also measured using CLM. It is concluded that doping the dolomitic-magnesite with 0.5 wt.% ilmenite leads to maximize rate of densification after firing for 4 h at only 1500 °C. Direct-bonded MgO-MgO network is shown enclosing merwinite and monticellite with minor magnesio-ferrite spinel solid solution ex-soluted within the periclase network. Due to the dense microfabric, the hydration resistance is enhanced 8 times compared with the un-doped samples. Also, there is deeper infiltration of the slag/refractory reaction products of the un-doped MgO-dolomite sample as compared with the doped one.

Thermal transformations of talc-carbonate rocks consisting of talc, chlorite, mica/illite, quartz, feldspar and calcite were investigated in the range of 900°-1100°C by X-ray diffraction, thermal analyses, scanning electron microscopy and energy dispersive spectroscopy. Microstructural changes of heated decarbonated samples were also investigated, and variations of some ceramic properties against temperature were followed. In the heated raw samples, olivine and enstatite together with merwinite were formed at T 1000°C, akermanite and monticellite were developed from talc, and shrinkage was almost unchanged. Heating of decarbonated samples yielded olivine and enstatite together with Mg-spinel on the expense of talc. In this case, a vitreous phase was also formed and shrinkage got increased. The neoformation processes in both the samples were discussed based on the SiO2-MgO-CaO and SiO2-Al2O3-MgO phase diagrams. Considering the magnitudes of the studied ceramic proper...

Hutcheonite (IMA 2013-029), Ca_3Ti_2(SiAl_2)O_(12), is a new garnet mineral that occurs with monticellite, grossular, and wadalite in secondary alteration areas along some cracks between primary melilite, spinel, and Ti,Al-diopside in a Type B1 Fractionation and Unidentified Nuclear effects (FUN) Ca-Al-rich inclusion (CAI) Egg-3 from the Allende CV (Vigarano type) carbonaceous chondrite. The mean chemical composition of type hutcheonite by electron probe microanalysis is (wt%) CaO 34.6, TiO_2 25.3, SiO_2 20.9, Al_2O_3 15.7, MgO 2.1, FeO 0.7, V_2O_3 0.5, total 99.8, giving rise to an empirical formula of Ca_(2.99)(Ti^(4+)_(1.53)Mg_(0.25)Al_(0.17)Fe^(2+)_(0.05)V^(3+)_(0.03))(Si_(1.68)Al_(1.32))O_(12). The end-member formula is Ca_3Ti_2(SiAl_2)O_(12). Hutcheonite has the Ia3d garnet structure with a = 11.843 A, V = 1661.06 A^3, and Z = 8, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.86 g/cm^3. Hutcheonite is a new secondary phase in Allende, apparently formed by iron-alkali-halogen metasomatic alteration of the primary CAI phases like melilite, perovskite, and Ti,Al-diopside on the CV chondrite parent asteroid. Formation of the secondary Ti-rich minerals like hutcheonite during the metasomatic alteration of the Allende CAIs suggests some mobility of Ti during the alteration. The mineral name is in honor of Ian D. Hutcheon, a cosmochemist at Lawrence Livermore National Laboratory, California, U.S.A.

A detailed mineralogical examination of representative material from the P2-West 'kimberlite' located in the Wajrakarur Kimberlite Field (India) demonstrates that significant differences exist between these rocks and archetypal hypabyssal kimberlite. The intrusion consists of an olivine-phyric facies which has been transected by, and includes clasts of, a consanguineous phlogopite-rich pegmatitic facies. The olivine-rich parts of P2-West are relatively fresh and consist of euhedral-to-subhedral microphenocrystal olivine set in a groundmass of fine-grained anhedral monticellite, amoeboid apatite, and subhedral-to-euhedral perovskite within a partially chloritized-to-fresh phlogopite-rich mesostasis. The rock lacks the abundant olivine macrocrysts characteristic of kimberlite. Monticellite crystals are commonly partially or completely replaced by pectolite and hydrogarnet. Similar material occurs as irregular aggregates randomly scattered throughout the groundmass. The groundmass, in contrast to that of hypabyssal kimberlites, is relatively poor in spinels. Atoll spinels are absent, with the majority of spinels occurring principally as mantles upon microphenocrystal olivine. Disaggregated cumulate-like assemblages of intergrown anhedral perovskite and spinel are common. Spinel compositions are unlike those of kimberlites and their evolutionary trend is similar to that of lamproite and lamprophyre spinels. The pegmatitic facies of the intrusion are highly and pervasively altered, and characterized by the presence of large clasts, veins, and irregular aggregates consisting of large (1–5 mm) crystals of pinkish-bronze Al-poor phlogopite intergrown with and/or including: apatite; pectolite-hydrogarnet pseudomorphs after an unidentified euhedral phase; chlorite laths; barytolamprophyllite; perovskite; tausonite; diverse Sr-Ba-carbonates; and baryte. The presence of barytolamprophyllite and tausonite are typical of potassic undersaturated alkaline rocks and have never been reported from kimberlite; however, neither feldspar nor feldspathoids are present in P2-West. Micas in fresh and altered rocks are Al2O3- and BaO-poor, and exhibit compositional evolutionary trends towards tetraferriphlogopite rather than kinoshitalite. On the basis of these mineralogical data it is suggested that P2-West represents an unusual lamproite-like intrusion which has undergone extensive hydrothermal deuteric alteration and should not be considered a bona fide kimberlite.

In this study we report P-rich olivine and the tric-calcium phosphate (TCP) stanfieldite in partially molten quartzphyllites from the ritual immolation site at the Goldbichl, near Innsbruck in the Tyrol, Austria. During partial melting, foamy patches of dark glassy material formed at the surface of the rocks and also as layers within the rocks. The pyrometamorphic rocks contain mostly the mineral assemblage olivine + orthopyroxene + plagioclase + spinel + glass. During the investigation of slag samples from this prehistoric ritual immolation site, extremely P-rich, apatite-bearing micro-domains were found. In these domains phosphoran olivine was found whose P contents are approaching the maximum P contents in olivine according to the experimental investigations of Boesenberg and Hewins (Geochim Cosmochim Acta 74:1923–1941, 2010). The textures within these domains indicate strongly disequilibrium conditions. The phosphoran olivines formed due to reactions involving apatite and the mineral assemblage of the quartzphyllites, and coexist with plagioclase and a tri-calcium phosphate phase (TCP) showing stanfieldite Ca4(Mg, Fe2+, Mn2+)5(PO4)6 composition. In terms of its chemical composition, olivine shows a wide range in composition with P ranging from 0.3 to 0.54 a.p.f.u, which corresponds to maximal 23 wt.% P2O5. These are the highest P-contents in olivine reported from rocks so far. The incorporation of P correlates with decreasing Si contents according to the charge balancing scheme $$ 2{{\mathrm{P}}^{5+ }}+□{{\mathrm{M}}_{1,2 }}=2\mathrm{S}{{\mathrm{i}}^{4+ }}+{{\left( {\mathrm{M}\mathrm{g},\mathrm{Fe}} \right)}^{2+ }}{{\mathrm{M}}_{1,2 }} $$ . Therefore P can only be incorporated in combination with a vacancy on the M1,2 position. Micro-Raman spectroscopy of phosphoran olivines indicates that these olivines can easily be identified with this method due to the strong signals of the SiO4 and PO4 vibrations. The external vibrations of the M1,2 sites at low wave-numbers are more complex than for P-free olivine. This might be due to the effect of P5+ on the M1 2+ and M2 2+ positions and the formation of vacancies on these sites. Since micro-Raman investigations of the TCP phase yielded no conclusive match with a known Raman spectrum of a phosphate mineral so far, therefore it is most likely that the TCP phase is stanfieldite, whose Raman spectrum has not been obtained yet. Schematical Schreinemakers analysis in the system CaO-Al2O3-FeO-SiO2-P2O5-H2O shows that P-rich olivine (fayalite-sarcopside solid solution) can form from mineral reactions involving chlorite, apatite and quartz and show that the occurrence of P-rich Fe-olivines spans a large T-range but is restricted to domains with high aSiO2. The mineral assemblage in the P-rich micro-domains shows that the formation of phosphoran olivine is not only restricted to the interaction between bone material and rocks in slags from ritual immolation sites as suggested by Tropper et al. (Eur J Mineral 16:631–640, 2004) from the immolation site in Oetz but can form locally due to the pyrometamorphic breakdown of a P-rich accessory precursor phase such as apatite.

A sulfide-type mineral of the district of Zimapan, Hidalgo, Mexico, was chemically and mineralogically analyzed with the aim of detecting minor species with added value for their subsequent beneficiation. Apart from the usual species of the site, the X-ray diffraction analysis (XRD) detected the presence of tungsten sulfate (WS2) and the mineral species typical of a base-metal sulfide site, as well as impurities such as: orthoclase, quartz, magnesium-silicon oxide, magnesioferrite, monticellite, andradite, magnetite and calcite, the latter being the mineral matrix. The Scanning Electron Microscopy (SEM) mapping confirmed the presence of the typical elements of the mineral: W, Si, O, Mg, Ca, C, Al, K, Fe, S, Zn and Cu. The Inductively Coupled Plasma Spectroscopy (ICP) analysis indicates an average concentration of 380 g W ton”1, as well as 1.81% Zn, 3.41% S, 0.15% Cu, 2.36% Fe, 0.78% Pb, 0.04% Mn, Sb 0.05% and 0.01% Ag. This mineral is a potential source for the extraction of tungsten

Two carbonatitic mineral assemblages, calcite + wollastonite and calcite + monticellite, which are encapsulated in two diamond grains from the Rio Soriso basin in the Juina area, Mato Grosso State, Brazil, were studied utilizing the NanoSIMS technique. The assemblages were formed as the result of the decomposition of the lower-mantle assemblage calcite + CaSi-perovskite + volatile during the course of the diamond ascent under pressure conditions from 15 to less than 0.8 GPa. The oxygen and carbon isotopic compositions of the studied minerals are inhomogeneous. They fractionated during the process of the decomposition of primary minerals to very varying values: δ18O from −3.3 to +15.4 ‰ SMOW and δ13C from −2.8 to +9.3 ‰ VPDB. These values significantly extend the mantle values for these elements in both isotopically-light and isotopically-heavy areas.

Investigation of the liquidus phase relations in the forsterite–diopside–enstatite system has been made at 7 GPa and variable temperatures under anhydrous condition using a Walker-type multi-anvil high pressure apparatus. A total of 16 compositions were synthesized to facilitate study of this system. Location of the piercing point on the forsterite–diopside bounding join has been established at Fo 39 Di 61 (all compositions are in wt.%) and 1980 ± 20 °C. Electron microprobe analyses of the phases indicate that forsterite ss can incorporate about 1 to 1.5 wt.% monticellite (CaMgSiO 4 ) in solid solution. In the diopside–enstatite join, a temperature minimum occurs at Di 66 En 34 and 1975 ± 30 °C, whereas the peritectic point, where orthopyroxene ss reacts with liquid to form clinopyroxene ss , occurs at En 65 Di 35 and 2010 ± 20 °C. The maximum amount of MgSiO 3 that can be incorporated in diopside ss has been measured to be about 82 wt.%. Because of the increase in the solid solution proportion of MgSiO 3 in diopside ss compared to that at 2 and 5.1 GPa, the peritectic point in the diopside–enstatite bounding join also shifts further toward the enstatite apex. In the ternary system, the invariant point has been located at Fo 54 Di 35 Q 11 and 2010 ± 30 °C, where orthopyroxene ss + forsterite ss + liquid ↔ clinopyroxene ss + forsterite ss + liquid occurs. Our present study confirms that the primary phase field of forsterite shrinks and that of clinopyroxene expands further in comparison to that observed at 2 and 5.1 GPa. Preliminary experimental results from composition Fo 80 Di 12 Qtz 8 with 4 wt.% Al 2 O 3 indicate that garnet (Pyrope 98 Grossularite 2 ) and forsterite (with 0.31 wt.% monticellite) are the liquidus phases, followed by clinopyroxene (Al 2 O 3 contents between 3.4 to 2.7 wt.%). At 1970 °C , the average composition of the liquids obtained through electron microprobe analysis was as follows: SiO 2 49.81, MgO 34.72, CaO 7.29, and Al 2 O 3 6.75 wt.%, which is somewhat similar to a komatiitic melt. When projected onto the forsterite–diopside–enstatite plane this liquid composition plots very close to our cotectic line. Taking model mantle composition of a garnet peridotite, a shift in the compositional path of the residual mantle materials has been determined after extraction of the volume percent of the melt using the Lever rule.

The meteorite impact that created the 32-km-wide Late Carboniferous West Clearwater structure, situated about 125 km east of the Hudson Bay arc, northern Quebec, formed a sheet of impact melt now exposed on a central ring of islands. We describe the textures and mineralogy of two xenoliths of partially metamorphosed limestone. These blocks represent recrystallized remnants of a cover of Middle Ordovician limestone, now completely eroded in the area. The fossiliferous dolomite-bearing limestone recrystallized to granoblastic calcite + periclase marble when the blocs landed in the sheet of impact-generated melt. The silica content of the marble led to the formation of a sanidinite-facies assemblage of unusual nesosilicates such as spurrite, merwinite, and monticellite. Aluminian srebrodolskite, Ca 2 (Fe 3+ ,Al) 2 O 5 , is found in material with a composition similar to “Portland cement clinker”. Phase equilibrium and stratigraphic data constrain the minimum peak conditions of metamorphism at T > 815°C, P X (CO 2 ) > 0.1. Retrograde mineral assemblages indicate that X (CO 2 ) dropped to less than 0.1 shortly after the peak of metamorphism. Portlandite and brucite formed during the late hydration of the assemblage upon cooling.

The Cambrian Snap Lake kimberlite, in the Northwest Territories, Canada, is a rare example of an economic, near-horizontal kimberlite dyke deposit with an average vertical thickness of ~2.5 m. The diamond deposit consists of hypabyssal serpentine monticellite kimberlite and contains volumetrically minor hypabyssal kimberlite breccias. The kimberlite is composed of serpentinized olivine set in the groundmass of serpentinized monticellite, serpentine, phlogopite, dolomite, spinel, apatite, rutile and ilmenite. The Snap Lake kimberlite is similar in major-element composition to Group-I kimberlite worldwide, yet has exceptionally low CaO and P 2 O 5 . The low Ca character of the kimberlite is evident in the absence of perovskite, low proportion of carbonate, and the occurrence of dolomite rather than calcite as the dominant groundmass carbonate. Three textural types of phlogopite present in the kimberlite (macrocrystic–microphenocrystic, large poikilitic groundmass phlogopite and small groundmass phlogopite) have distinct patterns of composition and zonation. Detailed studies of the zonation reveal a complex evolution of the phlogopite compositions from an early deep xenocrystal to two stages of groundmass crystallization. Superimposed on this evolution common to all kimberlites worldwide is an additional early stage of groundmass crystallization in which barian phlogopite was precipitated only in one part of the dyke. The crystallization of Ba-rich phlogopite is accompanied by Sr-rich apatite, Mn-rich ilmenite and Fe 3+ -rich rutile, and may be related to a highly localized influx of residual oxidized carbonatitic fluid. The deuteric origin of the fluid explains the Ca-poor character of the Snap Lake kimberlite and the formation of late carbonate-rich veins pervasively cross-cutting the dyke.

Kerimasi calciocarbonatite consists principally of calcite together with lesser apatite, magnetite, and monticellite. Calcite hosts fluid and S-bearing Na–K–Ca-carbonate inclusions. Carbonatite melt and fluid inclusions occur in apatite and magnetite, and silicate melt inclusions in magnetite. This study presents statistically significant compositional data for quenched S- and P-bearing, Ca-alkali-rich carbonatite melt inclusions in magnetite and apatite. Magnetite-hosted silicate melts are peralkaline with normative sodium-metasilicate. On the basis of our microthermometric results on apatite-hosted melt inclusions and forsterite–monticellite phase relationships, temperatures of the early stage of magma evolution are estimated to be 900–1,000°C. At this time three immiscible liquid phases coexisted: (1) a Ca-rich, P-, S- and alkali-bearing carbonatite melt, (2) a Mg- and Fe-rich, peralkaline silicate melt, and (3) a C–O–H–S-alkali fluid. During the development of coexisting carbonatite and silicate melts, the Si/Al and Mg/Fe ratio of the silicate melt decreased with contemporaneous increase in alkalis due to olivine fractionation, whereas the alkali content of the carbonatite melt increased with concomitant decrease in CaO resulting from calcite fractionation. Overall the peralkalinity of the bulk composition of the immiscible melts increased, resulting in a decrease in the size of the miscibility gap in the pseudoquaternary system studied. Inclusion data indicate the formation of a carbonatite magma that is extremely enriched in alkalis with a composition similar to that of Oldoinyo Lengai natrocarbonatite. In contrast to the bulk compositions of calciocarbonatite rocks, the melt inclusions investigated contain significant amount of alkalis (Na2O + K2O) that is at least 5–10 wt%. The compositions of carbonatite melt inclusions are considered as being better representatives of parental magma composition than those of any bulk rock.

Altres ajuts: FCT (SFRH / BD /11020/2002) In cases where the provenance of raw materials used in the manufacture of local archeological ceramics is of interest, a detailed study of thermal transformations of minerals may be useful. The purpose of this study was to measure mineralogical transformations of different types of clays obtained during experimental firing runs, carried out at different temperatures, with the main goal of establishing Algarve reference groups based on the composition of raw material and high-temperature mineralogy, which may be compared with ceramics in studies of provenance. Eleven samples of clay-rich raw materials from the Algarve Basin (southern Portugal) were fired to temperatures ranging from 300 to 1100°C in increments of 100°C under oxidizing conditions. These were chosen to have variable chemical and mineralogical compositions, representing the main compositional range of the clay deposits from the region. Mineralogical and geochemical characterizations of the original clays were carried out by X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. Mineral transformations on the fired products were also studied by XRD. Three groups of clays were distinguished according to the type of neoformed high-temperature minerals: (1) non-calcareous clays; (2) clays containing calcite as the only carbonate; and (3) clays with dolomite or dolomite + calcite. Firing of non-calcareous clays produced mullite at 1100-1200°C. Gehlenite and wollastonite formed by firing calcite-rich clays above 900°C, accompanied by anorthite or larnite in samples with small or large calcite contents, respectively. Firing of dolomite-rich clays at temperatures >900°C yielded a member of the gehlenite-åkermanite group and diopside. Anorthite, enstatite, periclase, forsterite, and monticellite may also form in the firing products.

The aim of this research was to investigate the effect of the chemical composition on the mechanical properties, bioactivity, and cytocompatibility in vitro of bioceramics in the MgO-CaO-SiO(2) system. Three single-phase ceramics (merwinite, akermanite and monticellite ceramics) with different MgO contents were fabricated. The mechanical properties were tested by an electronic universal machine, while the bioactivity in vitro of the ceramics was detected by investigating the bone-like apatite-formation ability in simulated body fluid (SBF), and the cytocompatibility was evaluated through osteoblast proliferation and adhesion assay. The results showed that their mechanical properties were improved from merwinite to akermanite and monticellite ceramics with the increase of MgO contents, whereas the apatite-formation ability in SBF and cell proliferation decreased. Furthermore, osteoblasts could adhere, spread and proliferate on these ceramic wafers. Finally, the elongated appearance and minor filopodia of cells on merwinite ceramic were more obvious than the other two ceramics.

The origin of alkali carbonates and chlorides in the groundmass of unaltered Udachnaya-East kimberlites in Siberia is still controversial. Contrary to existing dogma that the Udachnaya-East kimberlite was either contaminated by the crustal sediments or platform brines, magmatic origin of the groundmass assemblage has been proposed on the basis of melt immiscibility textures, melt inclusion studies, and strontium and neon isotope compositions. We further tested the idea of alkali- and chlorine enrichment of the kimberlite parental melt by studying olivine-hosted melt inclusions and secondary serpentine in kimberlites from the Slave Craton, Canada (Gahcho Kue, Jericho, Aaron and Leslie pipes) and southern West Greenland (Majuagaa dyke). Host olivine phenocrysts closely resemble groundmass olivine from the Udachnaya-East kimberlite in morphology, compositions (high-Fo, low-Ca), complex zoning with cores of varying shapes and compositions and rims of constant Fo. Melt inclusions in olivine consist of several translucent and opaque daughter phases and vapour bubble(s). The daughter crystals studied in unexposed inclusions by laser Raman spectroscopy and in carefully exposed inclusions by WDS-EDS are represented by Na-K chlorides, calcite, dolomite, magnesite, Ca-Na, Ca-Na-K and Ca-Mg-Ba carbonates, bradleyite Na3Mg(CO3)(PO4), K-bearing nahpoite Na2(HPO4), apatite, phlogopite and tetraferriphlogopite, unidentified sulphates, Fe sulphides, djerfisherite, pyrochlore (Na,Ca)2Nb2O6(OH,F), monticellite, Cr-spinel and Fe-Ti oxides. High abundances of Na, K (e.g., (Na+K)/Ca = 0.15-0.85) and incompatible trace elements in the melt inclusions are confirmed by LA-ICPMS analysis of individual inclusions. Heating experiments show that melting of daughter minerals starts and completes at low temperatures (~ 100oC and 600oC, respectively), further reinforcing the similarity with the Udachnaya-East kimberlite. Serpentine minerals replacing olivine in some of the studied kimberlites demonstrate elevated abundances of chlorine (up to 3-4 wt%), especially in the early generation. Despite heterogeneous distribution of chlorine such abundances are significantly higher than in the serpentine in abyssal and ophiolitic peridotites (

The matrix of volcaniclastic kimberlite (VK) from the Muskox pipe (Northern Slave Province, Nunavut, Canada) is interpreted to represent an overprint of an original clastic matrix. Muskox VK is subdivided into three different matrix mineral assemblages that reflect differences in the proportions of original primary matrix constituents, temperature of formation and nature of the altering fluids. Using whole rock X-ray fluorescence (XRF), whole rock X-ray diffraction (XRD), microprobe analyses, back-scatter electron (BSE) imaging, petrography and core logging, we find that most matrix minerals (serpentine, phlogopite, chlorite, saponite, monticellite, Fe–Ti oxides and calcite) lack either primary igneous or primary clastic textures. The mineralogy and textures are most consistent with formation through alteration overprinting of an original clastic matrix that form by retrograde reactions as the deposit cools, or, in the case of calcite, by precipitation from Ca-bearing fluids into a secondary porosity. The first mineral assemblage consists largely of serpentine, phlogopite, calcite, Fe–Ti oxides and monticellite and occurs in VK with relatively fresh framework clasts. Alteration reactions, driven by deuteric fluids derived from the juvenile constituents, promote the crystallisation of minerals that indicate relatively high temperatures of formation (> 400 °C). Lower-temperature minerals are not present because permeability was occluded before the deposit cooled to low temperatures, thus shielding the facies from further interaction with fluids. The other two matrix mineral assemblages consist largely of serpentine, phlogopite, calcite, +/− diopside, and +/− chlorite. They form in VK that contains more country rock, which may have caused the deposit to be cooler upon emplacement. Most framework components are completely altered, suggesting that larger volumes of fluids drove the alteration reactions. These fluids were likely of meteoric provenance and became heated by the volcaniclastic debris when they percolated into the VK infill. Most alteration reactions ceased at temperatures > 200 °C, as indicated by the absence or paucity of lower-temperature phases in most samples, such as saponite. Recognition that Muskox VK contains an original clastic matrix is a necessary first step for evaluating the textural configuration, which is important for reconstructing the physical processes responsible for the formation of the deposit.

The forsterite-bearing Type B (FoB) CAI SJ101 consists of three major structural units: (1) light patches of sector-zoned, poikilitic Al-rich clinopyroxene (Cpx) with numerous inclusions of small spinel grains and aggregates and subordinate amounts of Mg-rich melilite (Mel) and anorthite (An) (Sp–Cpx lithology), (2) dark sinuous bands of Al-rich clinopyroxene with large (up to ∼300 × 60 μm) poikilitically enclosed euhedral forsterite (Fo) crystals (Fo–Cpx lithology), and (3) the external Cpx–Sp–An rim overlying the entire inclusion. The two major lithologies are always separated by a transition zone of clinopyroxene poikilitically enclosing both forsterite and spinel. The patches of the Sp–Cpx lithology exhibit significant textural and mineralogical variability that is size-dependent. Small patches typically consist of Cpx and spinel with minor remnants of melilite and/or its alteration products. Large patches contain Mel–An-rich cores with either equigranular–ophitic–subophitic or ‘lacy’ textures reminiscent of those in Types B or C CAIs, respectively. All silicates poikilitically enclose numerous spinel grains of identical habit. Both melilite and anorthite gradually disappear toward the boundary with the Fo–Cpx lithology. Neither the evaporation mantle of Al-rich melilite typical of other FoBs nor the Wark–Lovering rim is present. Secondary minerals include grossular, monticellite, magnetite, and a few grains of wollastonite, andradite, and nepheline. Being a rather typical FoB mineralogically and chemically, texturally SJ101 differs from other FoBs in displaying the nearly complete segregation of forsterite from spinel which occur only in the Fo–Cpx and Sp–Cpx lithologies, respectively. The complex, convoluted internal structure of SJ101 suggests that the coarse-grained Sp–An–Mel–Cpx cores and Fo–Cpx lithology represent the precursor materials of FoBs, proto-CAIs and Fo-rich accretionary rims. While the inferred chemistry and mineralogy of the Fo-rich rims are fairly typical, the high Ak content in SJ101 melilite (78.7–82.3 mol.%) implies that the SJ101 proto-CAIs represent a new type of CAIs that has not been sampled before. This type of CAIs might have formed by remelting of spinel-rich condensates. The Group II REE pattern, slightly negative δ 29 Si and δ 25 Mg values, and nearly solar ratios of the major elements in the bulk SJ101 suggest that its precursors, proto-CAIs and Fo-rich rims, could have formed by a non-equilibrium condensation in a closed system of solar composition somewhat depleted in a super-refractory evaporation residue. The proposed formation scenario of SJ101 invokes a non-steady cooling and condensation of the nebular gas interrupted by at least two distinct melting episodes required to account for the igneous textures of the Mel–An–Cpx-rich cores (proto-CAIs) and the Fo–Cpx lithology.

A series of uncommon micro- and nano-inclusions has been identified in diamonds from the Rio Soriso placer deposit in Mato Grosso State, Brazil. The micro-inclusions are variable in size, from 1 to 300 µm. Usually, they are polymineralic, being formed predominantly by intergrowths of carbonates, silicates and other minerals. Carbonates are represented mostly by dolomite and occasionally by calcite. Silicates found are coesite, wollastonite-II, cuspidine and monticellite. Sulphides and ilmenite form micro-inclusions as well. Nano-inclusions are different from micro-inclusions not only in size (not exceeding 200 nm); they are usually included in micro-inclusions. Among nano-inclusions, halides (NaCl, KCl, CaCl2 and PbCl2), anhydrite, spinel, phlogopite, PbO2, TiO2 with an α-PbO2 structure, native Fe, and other phases are identified. All these minerals are of the eclogitic association: they are either associated with coesite or are included in a diamond with a light, ‘organic’ carbon isotopic composition (with δ 13C from − 14 to − 25‰ PDB). This confirms our earlier conclusion that diamonds from the Juina area may have formed as a result of subduction of the crustal material to depths of at least the lower transition zone or even the lower mantle. The pressure estimates for the investigated diamonds vary in a range from 3 to 10 GPa. An interesting assemblage of calcite + cuspidine + wollastonite + monticellite + fluid identified in one of the studied diamonds is considered as a product of a reaction of wollastonite + fluid forming cuspidine + monticellite. The presence of numerous pores, cavities and bubbles in mineral inclusions, and identification of an association of volatile-containing mineral inclusions, such as halides (NaCl, KCl, CaCl2, and PbCl2), fluorine-containing silicate cuspidine, and phlogopite emphasize the important role of volatiles, particularly chlorine and fluorine in the formation of the diamonds.

Mineralogical transformations during firing of two extremely calcareous clays, one calcite and other dolomite rich, and relatively poor in silica were studied. Original clays were mineralogical and chemically characterized with X-ray diffraction (XRD) and X-ray fluorescence (XRF). Firing of both clays was carried out in the temperature range 300–1100 °C under oxidizing conditions and the mineralogical transformations were investigated with XRD, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy associated with energy dispersive X-ray spectroscopy (SEM-EDS). Important compositional differences in the neoformed phases were observed between calcite and dolomite rich clays. In the Ca-rich clay the assemblage gehlenite + wollastonite + larnite was observed. In the Mg(Ca)-rich clay the reaction products included akermanite, diopside, monticellite, forsterite, periclase and spinel. XRD and SEM-EDS showed the presence, in both clays, of a potassium–calcium sulfate in samples fired between 900 and 1100 °C.

The Majuagaa kimberlite dike in the Maniitsoq region, southern West Greenland, is 564 Ma old, 2.5 km long, and up to 2 m wide. It is well exposed and very fresh, allowing detailed petrographic and chemical investigations. Little or no serpentinization is observed, and primary petrographic characteristics and grain morphologies are preserved. The dike is diamondiferous and carries xenoliths (up to 30 cm), megacrysts and macrocrysts characteristic of kimberlite. On the bases of the paragenesis and compositions of groundmass phlogopite, geikielite and Mg–Ti-enriched spinel, the dike is classified as kimberlite, despite being carbonate-rich and the apparent absence of monticellite characteristic of many occurrences of bona fide hypabyssal kimberlite. Olivine megacrysts, macrocrysts and microcrysts are all xenocrystic, whereas microphenocrysts are xenocrystic microcrysts overgrown by equilibrium olivine. Most olivine (max. 37 wt.%) is found to be xenocrystic on the basis of Ni mass balance. The average bulk composition of the melt involved in the dike compares well with Group-1 kimberlite. Corrected for xenocrystic olivine and ilmenite, the melt has the composition of a silicocarbonatite and compares with experimental melts formed at very low degrees of partial melting of CO2-bearing lherzolite.

Most chondritic materials experienced diverse styles of secondary alteration resulting in formation of hydrous and anhydrous oxygen-bearing minerals—silicates, oxides, and carbonates (phyllosilicates, magnetite, calcite, dolomite, breunnerite, ferrous olivine, hedenbergite, wollastonite, grossular, monticellite, forsterite, andradite, nepheline, sodalite) (Brearley 2003, 2005 and references therein). Petrographic, mineralogic, oxygen and short-lived isotope systematics (26Al-26Mg, 53Mn-53Cr, 129I-129Xe) suggest that alteration occurred in the presence of aqueous solutions under variable physico-chemical conditions (temperature, water:rock ratio, pH, f O2, and fluid compositions) in an asteroidal setting; it started within 1–2 m.y. after formation of the CV CAIs, was multistage, and lasted up to 15 m.y. (Krot et al. 2006 and references therein). Here we review bulk O-isotopic compositions of chondritic materials, O-isotopic compositions of secondary minerals produced during asteroidal alteration, and possible effects of fluid-assisted thermal metamorphism on O-isotopic exchange in primary, high-temperature minerals (melilite and anorthite) in the CV and CO CAIs. The implications of these data for understanding temperatures of alteration, water:rock ratios, and oxygen isotopic composition of water, that probably accreted into chondrite parent bodies in the form of ice, are discussed. The inferred or measured O-isotopic composition of the meteoritic water is close to the terrestrial fractionation line (Δ17O = ±2‰); it is very different from the inferred O-isotopic compositions of the Sun [Δ17O ~ −25‰] (Clayton 2002; Yurimoto and Kuramoto 2004; Hashizume and Chaussidon 2005; Lyons and Young 2005), suggesting significant evolution of O-isotopic composition of the gaseous reservoir in the inner protoplanetary disk over its short (~3–5 m.y.) life time.

Constraining the composition of primitive kimberlite magma is not trivial. This study reconstructs a kimberlite melt composition using vesicular, quenched kimberlite found at the contact of a thin hypabyssal dyke. We examined the 4 mm selvage of the dyke where the most elongate shapes of the smallest calcite laths suggest the strongest undercooling. The analyzed bulk compositions of several 0.09–1.1 mm 2 areas of the kimberlite free from macrocrysts were considered to be representative of the melt. The bulk analyses conducted with a new ‘‘chemical point-counting’’ technique were supplemented by modal estimates, studies of mineral compositions, and FTIR analysis of olivine phenocrysts. The melt was estimated to contain 26– 29.5 wt% SiO2, � 7 wt% of FeOT, 25.7–28.7 wt% MgO, 11.3–15 wt% CaO, 8.3–11.3 wt% CO2, and 7.6–9.4 wt% H2O. Like many other estimates of primitive kimberlite magma, the melt is too magnesian (Mg# = 0.87) to be in equilibrium with the mantle and thus cannot be primary. The observed dyke contact and the chemistry of the melt implies it is highly fluid (g =1 0 1 –10 3 Pa s at 1100–1000 � C) and depolymerized (NBO/T = 2.3–3.2), but entrains with 40–50% of olivine crystals increasing its viscosity. The olivine phenocrysts contain 190–350 ppm of water suggesting crystallization from a low SiO2 magma (aSiO2 below the olivine-orthopyroxene equilibrium) at 30–50 kb. Crystallization continued until the final emplacement at depths of few hundred meters which led to progressively more Ca- and CO2-rich residual liquids. The melt crystallised phlogopite (6–10%), monticellite (replaced by serpentine, � 10%), calcite rich in Sr, Mg and Fe (19–27%), serpentine (29–31%) and

The results of a complex study of melt inclusions in olivine phenocrysts contained in unaltered kimberlites from the Udachnaya-East pipe indicate that the inclusions were captured late during the magmatic stage, perhaps, under a pressure of

International audience; A shallow-level dioritic pluton of Upper Cretaceous age caused extensive contact metamorphism of a Mesozoic calcareous sequence at Oraviţa-Ciclova in Romania. The peak metamorphic assemblage (stage I) includes wollastonite, åkermanite-rich melilite, Ti-rich calcic garnet, and pyrrhotite. A second, subsequent paragenesis (stage II) is due to local decreases in fluid pressure and includes gehlenite, Ti-poor calcic garnet, monticellite, Al-rich diopside, magnetite, perovskite, and probably a Ca-Si mineral (kilchoanite?). An early hydrothermal stage (stage III) produced retrogression of the first two stages and a paragenesis including vesuvianite, clintonite, fukalite, katoite, and hydroxylellestadite. A second, late hydrothermal event (stage IV) resulted in the formation of clinochlore, talc, epidote, zeolites (scolecite and thomsonite-Ca), thaumasite, and tobermorite. A last, weathering, paragenesis corresponding to stage V includes allophane (C-S-H gels) and probably portlandite, unpreserved because of its transformation to aragonite, then calcite. The peak metamorphic conditions during the prograde evolution are estimated to have been 750–800 °C for a fluid pressure of up to 0.5 kbar. The main constants determined from chemical, optical, and X-ray powder analyses of these mineral species are reported here. This work documents the first occurrence of katoite and the second occurrences of perovskite, fukalite, and hydroxylellestadite in the Romanian skarns.

Minerals of olivine–melilite and olivine–monticellite rocks from the Krestovskiy massif contain primary silicate-salt, carbonate-salt, and salt melt inclusions. Silicate-salt inclusions are present in perovskite I and melilite. Thermometric experiments conducted on these inclusions at 1,230–1,250°C showed silicate–carbonate liquid immiscibility. Globules of composite carbonate-salt melt rich in alkalies, P, S, and Cl separated in silicate melt. Carbonate salt globules in some inclusions from perovskite II at 1,190–1,200°C separated into immiscible liquid phases of simpler composition. Carbonate-salt and salt inclusions occur in monticellite, melilite, and garnet and homogenize at close temperatures (980–780°C). They contain alkalies, Ca, P, SO3, Cl, and CO2. According to the ratio of these components and predominance of one of them, melt inclusions are divided into 6 types: I—hyperalkaline (CaO/(Na2O+K2O)≤1) carbonate melts; II—moderately alkaline (CaO/(Na2O+K2O)>1) carbonate melts; III—sulfate-alkaline melts; IV—phosphate-alkaline melts; V—alkali-chloridic melts, and VI—calc-carbonate melts. Joint occurrence of all the above types and their syngenetic character were established. Some inclusions demonstrated carbonate-salt immiscibility phenomena at 840–800°C. A conclusion in made that the origin of carbonate melts during the formation of intrusion rocks is related to silicate–carbonate immiscibility in parental alkali-ultrabasic magma. The separated carbonate melt had a complex alkaline composition. Under unstable conditions the melt began to decompose into simpler immiscible fractions. Different types of carbonate-salt and salt inclusions seem to reflect the composition of these spatially isolated immiscible fractions. Liquid carbonate-salt immiscibility took place in a wide temperature range from 1,200–1,190°C to 800°C. The occurrence of this kind of processes under macroconditions might, most likely, cause the appearance of different types of immiscible carbonate-salt melts and lead to the formation of different types of carbonatites: alkali-phosphatic, alkali-sulfatic, alkali-chloridic, and, most widespread, calcitic ones.

Microstructural analysis of MgO—MgAl2O4 refractory bricks corroded at 1400–1450°C by calcium aluminosilicate slag reveals secondary spinel, monticellite, merwinite, and MgO as microscopic corrosion products, generally forming in this sequence as the brick is penetrated. The secondary spinel forms an incomplete layer close to (but not at) the MgO grain. Thermodynamic calculations are used to support a detailed model of the corrosion mechanism.

Lapilli and spatter of natrocarbonatite extruded from the T56B cone of Oldoinyo Lengai (Tanzania) in August 2003 are unusually rich in apatite, silicate, oxide and sulphide minerals. These minerals occur primarily within inclusions of quenched natrocarbonatite in gregoryite and fractures in nyerereite-gregoryite intergrowths. Silicates include members of the sodian cuspidine–niobian cuspidine–niocalite solid-solution series and manganoan monticellite. Oxides are represented by members of the magnesioferrite–jacobsite–magnetite solid-solution series. Sulphides occurring in decreasing order of abundance include: ferroan alabandite, manganoan ferroan sphalerite, galena and pyrrhotite. Petrographic and compositional data for these minerals are interpreted to indicate that all are high-temperature (

Crystallization temperatures (T) and oxygen fugacities (fO2 )o f kimberlite magma are estimated from oxides included in olivine phenocrysts from the Leslie, Aaron, Grizzly and Torrie kimberlite pipes in the central Slave Province, Canada. Crystallization temperatures recorded by olivine–chromite pairs at an assumed pressure of 1� 0 GPa are 1030–1170 � C � 50 � C, with a mean of � 1080 � C. At these temperatures, the fO2 of coexisting olivine and chromite is 2–3 log units less oxidized than the nickel–nickel oxide (NNO) buffer at a silica activity limited by the presence of monticellite. Mass balance of olivine, bulk-rock and liquid compositions in equilibrium with olivine phenocryst rims suggests that these kimberlites represent crystallization from a magma with 11–28 mol % of liquid, 10 mol % of earlier precipitated olivine phenocrysts and 62–79 mol % of mantle xenocryst olivine. The calculated T–fO2 values indicate that diamonds entrained in the Lac de Gras kimberlites were probably transported to the surface within the stability field of graphite but close to the graphite–CO2 boundary.

Oxygen isotope compositions and fractionations between calcite (Cc) and magnetite (Mt), diopside-rich clinopyroxene (Di), monticellite (Mnt), kimzeyite-rich garnet (Gt), and biotite (Bt) were measured for carbonatites from Oka (Canada), Magnet Cove (USA), Jacupiranga (Brazil), and Essonville (Canada), to obtain crystallization temperatures and explore the crystallization history of carbonatites. The highest isotopic temperatures are obtained from Cc–Mt fractionations from Oka (745–770 °C) and Cc–Mnt fractionations from Magnet Cove (700 and 760 °C). Cc–Mt temperatures for very coarse-grained, euhedral magnetite phenocrysts and calcite from Jacupiranga are 700 °C. In samples that contain diopside and magnetite, the Cc–Mt temperatures are always higher than Cc–Di temperatures. This difference is consistent with crystallization of magnetite before diopside, minor retrograde resetting of magnetite isotopic compositions, and the order of crystallization inferred from inclusions of Mt in Di. Cc–Mt, Cc–Di, and Cc–Mnt fractionations are thus interpreted to represent those established during crystallization at rapid cooling rates (103–104 °C/my). Diffusion model calculations indicate that at slower post-crystallization cooling rates (10–102 °C/my), magnetite compositions should experience significant isotopic resetting by diffusional exchange with Cc, Bt, and apatite, and yield lower temperatures than Cc–Di. Cc–Bt fractionations correspond to the lowest temperatures (440–560 °C). Although some of these are relatively high isotopic temperatures for biotite, they most likely represent those established during subsolidus retrograde exchange between biotite and calcite during rapid subsolidus cooling.

Carbonatite magmas precipitate silicates, in addition to the abundant carbonates, oxides, and phosphates. Calculated silica activities for equilibria involving silicates and a silica component in magmatic liquids predict specific assemblages for silicate and oxide phases in carbonatites. These assemblages provide tests of alternative sources (carbonatite magma, coeval silicate magma, or older rock) for silicate minerals in carbonatites. Quartz, feldspars, and orthopyroxene are unlikely to be primary magmatic phases in carbonatites, because the silica activity in carbonatite magmas is too low to stabilize these minerals. Zircon and titanite should be unstable relative to baddeleyite and perovskite, respectively, but they do occur in carbonatites. Liquids dominated by carbonate are strongly nonideal with respect to dissolved silica. Consequently, activity coefficients for a silica component in carbonatite liquids are >>1, so that small mole fractions of SiO2 translate into silica activities sufficient to stabilize phlogopite, clinopyroxene, amphibole, monticellite, and forsterite, among other silicates. Examination of silicate mineral assemblages in carbonatites in the light of silica activity indicates that many carbonatites are contaminated by solid silicate phases from external sources but these xenocrysts can be discriminated from magmatic minerals.

Calc-silicate xenoliths occur as part of a xenolith and autolith swarm in the Lower Zone of the Kiglapait Intrusion, Labrador. All xenoliths are lighter-colored than the local troctolite host rock, and are surrounded by a 1–2 cm thick reaction zone of clinopyroxenite. The typical mineral assemblage in calc-silicate xenoliths is diopside + forsterite + monticellite + spinel, and one also contains akermanite. Reaction zones are dominated by diopside and spinel. All clinopyroxene compositions are “fassaitic,” with high concentrations of Al 2 O 3 (4–12 wt%), TiO 2 (1–4 wt%), and calculated Fe 2 O 3 (Fe 3+ > Fe 2+ ). In addition, clinopyroxene grains locally display extreme zoning in Si, Al, Ti, and X Mg . Akermanite contains up to 1.5 wt% Na 2 O. Textures in the xenoliths are complex, with most containing highly irregular intergrowths of diopside, forsterite, and monticellite. Akermanite and forsterite are separated locally by a coarse symplectic intergrowth of diopside and monticellite, which resulted from a retrograde reaction. The dominant assemblage probably represents the production of monticellite from calcite + clinopyroxene + forsterite, until calcite was consumed. These reactions require metamorphic temperatures of ~900 °C and pressures ≤ 0.4 kbar, such that the xenoliths were probably derived from the roof of the magma chamber. Whole-rock compositions reflect either substantial chemical exchange with the Kiglapait magma, or a very impure dolomitic protolith. The clinopyroxenite reaction zones were produced primarily by assimilation of carbonate by the Kiglapait magma, in combination with the effects of magma undercooling near the xenoliths.

The state-of-the-art in the field of creation and use of spinel, spinel-forming, and corundum-spinel concretes in the world is analyzed. In contrast to foreign-made concretes of this calss produced using high-alumina cement Russian specialists have developed cementless spinel concretes of the type of ceramic castables. Achievements in the field of low-cement self-flowing (cast) concretes, which are often more effective than vibrocompacted ones, are considered. The factors that determine their quality are analyzed. Concretes of this class can be obtained on the base of ceramic binders (HCBS). Due to their diminished (compared to low-cement concretes) water demand the materials can possess a lower porosity.

Isotopic compositions of the noble gases (He, Ne, Ar, Kr, Xe) were obtained by stepwise heating of separated mineral phases from carbonatites from Brazil (Jacupiranga, Tapira) and Canada (Borden, Oka, and Prairie Lake) as well as one syenite (Poohbah Lake, Canada). Mineral phases used were apatite, forsterite, diopside, calcite, monticellite, and perovskite. Large amount of in situ produced 238U-fissiogenic 131–136Xe, along with lesser amounts of 238U-fissio-genic 83–86Kr and in situ 4He were found in most samples. An apatite sample from the Prairie Lake carbonatite showed a 136Xe130Xe ratio of about 1400. Some samples, mostly apatites, showed excess 129Xe relative to air in the high temperature (1800°C) gas fractions. The highest 129Xe130Xe ratios, between 7.0 and 8.6, are similar to those found in other mantle-derived materials such as MORBs and diamonds. The excess `Xe is considered to be primordial and attributed to now extinct nuclide 129I once present in the early history of the Earth. Neon isotopic compositions were also anomalous showing very low 20Ne22Ne ratios (down to 0.01) and high 21Ne22Ne ratios (up to 1.25). They are attributed to Wetherill reactions, such as 18O(α,n)21Ne, 19F(α,n)22Na(β+)22Ne, and so on. The measured 40Ar/36Ar ratios are extremely variable and range from values that are close to atmospheric to values as high as 42400. Stepwise heating studies of an apatite from the Jacupiranga carbonatite indicate that the high temperature fractions retain the original noble gas signature of the carbonatite source. The 40Ar/36Ar ratios for the high temperature gas fractions are about 6400 or smaller. A plot of 40Ar/36Ar vs. 129Xe/130Xe shows that the source of carbonatites is different and less degassed than that of MORBs. The presence of excess 129Xe in carbonatites suggests that carbon in carbonatites is unlikely to be recycled C related to subduction processes.

We used the Panurge ion microprobe to measure concentrations of the rare earth elements (REEs), Ba, Hf, and Sr in melilite, clinopyroxene, plagioclase, and perovskite and Mg isotopes in plagioclase, spinel, melilite, fassaite, hibonite, grossular, and monticellite from the Allende Type B1 calcium-, aluminum-rich inclusion (CAI), USNM 3655A. The distribution and concentration of Ba and the REE in melilite from the melilite-rich mantle of 3655A are unlike those predicted from melilite-melt REE partitioning experiments for closed system crystal fractionation. REE concentrations are lower than expected in the first crystallized gehlenitic melilite, increase rapidly to higher than expected concentrations in melilite with intermediate akermanite contents (Ak30–Ak40), and decrease as expected only during the late stage of mantle crystallization. Barium concentrations in melilite are 10–50 times those expected, and the LREE/HREE ratio increases continuously rather than remaining constant. The unexpected distribution of trace elements in melilite reflects a progressive enrichment of trace elements in the melt during the early stages of crystallization. A partial explanation for this observation is the dissolution of precursor perovskite that contained half or more of the total REE budget of the inclusion. In addition, there are large trace element enrichments adjacent to included spinel in melilite and similar but smaller enrichments adjacent to spinet in clinopyroxene. These enrichments are consistent with the existence of trace element enriched boundary layers at the mineral/melt interfaces. The fact that kinetic processes partially control trace element abundances and distributions suggests rapid cooling during crystallization of the melilite-rich mantle. Similar trace element signatures are ubiquitous in Type B1 CAI, suggesting that each experienced a similar thermal history. The Mg isotope record of 3655A is distinguished by four salient features: (1) large ^(26)Mg excesses correlated with the respective AI/Mg ratios in plagioclase, melilite, and hibonite, (2) F_(Mg), the mass-dependent fractionation of Mg, is positive, with enrichment of the heavier Mg isotopes in all primary phases, (3) a heterogeneous distribution of F_(Mg) values, with F_(Mg) in melilite systematically greater than in either spinel or fassaite, and (4) isotopically normal Mg in the secondary alteration phases, grossular and monticellite. The occurrence of ^(26)Mg^∗, the decay product of ^(26)Al, in anorthite implies early formation of 3655A, while ^(26)Al was extant at nearly the canonical solar system value of ∼5 × 10^(−5). The trace element and Mg isotope heterogeneities suggest a formation scenario for 3655A which includes (1) flash heating to partially melt a solid precursor, (2) rapid cooling to allow survival of relict phases, (3) diffusive exchange of Mg between melilite and a nebular reservoir, and (4) alteration at low temperature. Although this model explains most of the trace element and isotopic characteristics of 3655A and other Type BI CAIs, it does not provide an explanation for the rapid change of LREE/HREE ratios of melilite during crystallization.

The paper examines the compositions and properties of clay body mixes based on multimineral and secondary raw materials for the manufacture of facing tile. The optimal amounts and ratios are established for oxides of the RO and R2O types. It is revealed that the mineral composition of the body mix has a strong bearing on the structure and properties of the tile.

During liquid-phase sintering (LPS) a large number of transport mechanisms occur simultaneously. Most often the microstructure of the sintered product provides information on these mechanisms. Previous studies on the infiltration of dense, polycrystalline MgO by a silicate liquid were aimed at investigating microstructural development as a function of the volume-fraction of the liquid. In this paper results on the early stages of the liquid infiltrating the compact are presented. A unique experimental technique has been developed that permits microstructural comparison of the same grains before and only minutes after the start of infiltration. Qualitative results on microstructural developments such as grain-growth, grain-morphology and changes in the chemistry of the liquid are presented in this work. The choice of composition of the liquid was monticellite (CaMgSiO{sub 4}) which is in thermodynamic equilibrium with MgO at 1,700 C and is a commonly observed intergranular composition in LPS MgO.

Single-crystal X-ray diffraction data have been obtained at several pressures to 5.6 GPa for synthetic LiScSi04 olivine. The bulk modulus is 118 :t I GPa, assuming K' = 4. This value is smaller than that of forsterite because compressibility of Li-O bonds in the M1 octahedral site is approximately twice that of the MP+-O bonds in other isomorphs. Compressibilities of a, b, and c orthorhombic axes are 2.70, 2.80, and 2.61 (all x 10-3 GPa-1), respectively. This nearly isotropic compression (axial compression ratios = 1.00: 1.04:0.97) contrasts with that offorsterite (1.00: 1.99:1.55), fayalite (1.00:2.83: 1.22), monticellite (1.00: 1.85:1.10), and chrysoberyl (1.00: 1.30:1.17). These differences arise from the distinctive distribution of cations of different valences and consequent differences in M 1-0 and M2-0 bond compressibilities. The Li M 1 octahedron displays a significant decrease in polyhedral distortions with pressure, a behavior not observed in other olivines.

Fluid inclusions in apatite, monticellite, and calcite from the Oka carbonatite complex generally comprise either aqueous liquid + vapour or aqueous liquid + vapour + halite. Some inclusions also contain a variety of trapped solids, including calcite, strontianite, nahcolite, and mirabilite. Microthermometry and Raman spectroscopy indicate that CO2 is not an important constituent of these fluids. Microthermometric data also indicate that the hydrothermal fluids liberated from the carbonatitic magma had a wide range of salinities (4.2 to 49 eq. wt% NaCl) and densities (0.77 to 1.26 g/cm3). Most of the fluids had relatively low concentrations of SO42− and CO32− (