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In the selective reduction process of lateritic nickel ore, the formation of the liquidus phase could be obtained by increasing the temperature and additive, resulting in an uneconomic process. Nevertheless, it could also be obtained by modifying the ore basicity by adding low-cost fluxes, such as CaO, SiO2, MgO, and Al2O3. In this work, the effect of three types of basicity (binary, ternary, and quaternary) in selective reduction of saprolitic nickel ore on metallic grade and recovery, phase transformation, and microstructure of ferronickel was investigated clearly. The nickel ore, sodium sulfate, coal, and flux mixture was reduced to 1150 °C for 60 min. Then, the wet magnetic separation process was continued to separate ferronickel from impurities. The result showed that the optimum basicity for the selective reduction of saprolitic nickel ore was 0.6 of ternary basicity (CaO + MgO/SiO2), modified by CaO addition. It produced 16.11% and 50.57% for nickel grade and recovery in concentrate, respectively. Modified basicity with CaO addition is more effective than MgO, Al2O3, and SiO2 addition due to its ability to break the forsterite structure and release iron and nickel. It also could be reacted with magnesium silicate structure to form calcium–magnesium silicate structure such as melilite and monticellite.

Focused on uncoated ceramics, this tutorial paper is divided into two main sections. The first section deals with the operational phases required prior to firing (drying, piling, fuel supply). Then, the second chapter deals with the transformations that occur in the clayey paste during firing. An overall understanding of the firing process includes several issues to be considered and properly investigated. Thereafter, the thermal behaviour of several mineralogical phases (calcite and dolomite; quartz and cristobalite; K-feldspar and plagioclase; rutile and anatase; haematite, maghemite, hercynite and metallic Fe; illite, muscovite, biotite and chlorite; wollastonite, melilite, anorthite and monticellite; diopside and kaolinite) is described. Four brief chapters are further dedicated to the development of the amorphous/glassy component, to the matrix and its porosity, to the colour and the organic matter and to the variations in chemical composition, respectively. The concluding remarks provide a short list of the analytical techniques that have been commonly applied to the investigation of firing conditions and a concise summary of the state of the art of the “firing issue”. The method to be applied in future experimental reproductions and the opportunity itself to investigate the “firing issue” in various contexts are further discussed.

Processing of magnesia based ceramic by unidirectional dry pressing from Moroccan magnesite is described. The applied magnesite was characterized in terms of its composition, granulometric analysis, surface specific area, and thermal behavior. After appropriate processing, the prepared specimens were fired at various temperatures up to 1350 °C to study the ceramic properties. The ceramic material resulted after firing was investigated regarding the phases composition, structural characteristics, and physical properties of technological interest. On this way, the production of materials having interesting properties such as shrinkage, porosity, density, flexural strength, toughness, dielectric constant, and thermal conductivity is achieved. An X-ray diffraction (XRD) analysis showed that the ceramic sample is composed of periclase as major phase and monticellite and calcium alumino-ferrite as minor phases. The content of amorphous phase that governs the sample properties varies between 26.5 and 31%. Thermal shock tests realized in water showed that the ceramic sample presents good thermal shock resistance. The results revealed that Moroccan magnesite has qualities necessary for the manufacture of ceramic products.

We present petrographic and mineral chemical data for a suite of samples derived from the De Beers dyke, a contemporaneous, composite intrusion bordering the De Beers pipe (Kimberley, South Africa). Petrographic features and mineral compositions indicate the following stages in the evolution of this dyke: (1) production of antecrystic material by kimberlite-related metasomatism in the mantle (i.e., high Cr-Ti phlogopite); (2) entrainment of wall-rock material during ascent through the lithospheric mantle, including antecrysts; (3) early magmatic crystallisation of olivine (internal zones and subsequently rims), Cr-rich spinel, rutile, and magnesian ilmenite, probably on ascent to the surface; and (4) crystallisation of groundmass phases (i.e., olivine rinds, Fe-Ti-rich spinels, perovskite, apatite, monticellite, calcite micro-phenocrysts, kinoshitalite-phlogopite, barite, and baddeleyite) and the mesostasis (calcite, dolomite, and serpentine) on emplacement in the upper crust. Groundmass and mesostasis crystallisation likely forms a continuous sequence with deuteric/hydrothermal modification. The petrographic features, mineralogy, and mineral compositions of different units within the De Beers dyke are indistinguishable from one another, indicating a common petrogenesis. The compositions of antecrysts (i.e., high Cr-Ti phlogopite) and magmatic phases (e.g., olivine rims, magnesian ilmenite, and spinel) overlap those from the root zone intrusions of the main Kimberley pipes (i.e., Wesselton, De Beers, Bultfontein). However, the composition of these magmatic phases is distinct from those in ‘evolved’ intrusions of the Kimberley cluster (e.g., Benfontein, Wesselton water tunnel sills). Although the effects of syn-emplacement flow processes are evident (e.g., alignment of phases parallel to contacts), there is no evidence that the De Beers dyke has undergone significant pre-emplacement crystal fractionation (e.g., olivine, spinel, ilmenite). This study demonstrates the requirement for detailed petrographic and mineral chemical studies to assess whether individual intrusions are in fact ‘evolved’; and that dykes are not necessarily produced by differentiated magmas.

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.

In this research, high-pure monticellite ceramic (CaMgSiO4) nanoparticles were synthesized via a novel sol–gel method using ethanol and chloride ions for the acceleration of polycondensation process. The gel obtained from metal alkoxide and metal salts precursors dried at 100°C; then, the dried-gel calcined at different temperatures to monitor the structural development of the final samples. The effect of various heat-treatment temperatures on the x-ray diffraction patterns, followed by the calculations from scherrer’s equation, showed that the grain size of the synthesized samples at 1200°C was around 28 nm. Based on dynamic light scattering spectroscopy, the size of most of the particles was ~85 nm. Williamson–Hall formula was also used to calculate the lattice strain of the samples. According to the results, by changing the heat-treatment temperature, lattice strain/stress, lattice parameters and grain size have meaningfully changed. The proposed synthesis method showed superior advantages in comparison with the other conventional techniques presented in the literature, which is relatively faster at lower temperatures. The synthesized high-pure monticellite nanoparticles could be applied in different biomedical engineering applications in which the purity and structural properties are of importance, such as dental, bone tissue engineering, coatings on biomedical implants, surgery hemostasis and inducing osteogenesis in vivo applications.

The Letseng-la-Terae kimberlite (Lesotho), famous for its large high-value diamonds, has five distinct phases that are mined in a Main and a Satellite pipe. These diatreme phases are heavily altered but parts of a directly adjacent kimberlite blow are exceptionally fresh. The blow groundmass consists of preserved primary olivine with Fo86−88, chromite, magnesio-ulvospinel and magnetite, perovskite, monticellite, occasional Sr-rich carbonate, phlogopite, apatite, calcite and serpentine. The bulk composition of the groundmass, extracted by micro-drilling, yields 24–26 wt% SiO2, 20–21 wt% MgO, 16–19 wt% CaO and 1.9–2.1 wt% K2O, the latter being retained in phlogopite. Without a proper mineral host, groundmass Na2O is only 0.09–0.16 wt%. However, Na-rich K-richterite observed in orthopyroxene coronae allows to reconstruct a parent melt Na2O content of 3.5–5 wt%, an amount similar to that of highly undersaturated primitive ocean island basanites. The groundmass contains 10–12 wt% CO2, H2O is estimated to 4–5 wt%, but volatiles and alkalis were considerably reduced by degassing. Mg# of 77.9 and 530 ppm Ni are in equilibrium with olivine phenocrysts, characterize the parent melt and are not due to olivine fractionation. 87Sr/86Sr(i) = 0.703602–0.703656, 143Nd/144Nd(i) = 0.512660 and 176Hf/177Hf(i) = 0.282677–0.282679 indicate that the Letseng kimberlite originates from the convective upper mantle. U–Pb dating of groundmass perovskite reveals an emplacement age of 85.5 ± 0.3 (2σ) Ma, which is significantly younger than previously proposed for the Letseng kimberlite.

Homogeneous single crystals of synthetic monticellite with the composition $${\text{Ca}}_{0.88}{\text{Mg}}_{1.12}{\text{SiO}}_4$$ (Mtc I) were annealed in a piston-cylinder apparatus at temperatures between 1000 and $$1200\,^{\circ }\hbox {C}$$ , pressures of 1.0–1.4 GPa, for run durations from 10 min to 24 h and applying bulk water contents ranging from 0.0 to 0.5 wt% of the total charge. At these conditions, Mtc I breaks down to a fine-grained, symplectic intergrowth. Thereby, two types of symplectites are produced: a first symplectite type (Sy I) is represented by an aggregate of rod-shaped forsterite immersed in a matrix of monticellite with end-member composition (Mtc II), and a second symplectite type (Sy II) takes the form of a lamellar merwinite–forsterite intergrowth. Both symplectites may form simultaneously, where the formation of Sy I is favoured by the presence of water. Sy I is metastable with respect to Sy II and is successively replaced by the latter. For both symplectite types, the characteristic spacing of the symplectite phases is independent of run duration and is only weeakly influenced by the water content, but it is strongly temperature dependent. It varies from about 400 nm at $$1000\,^{\circ }\hbox {C}$$ to 1200 nm at $$1100\,^{\circ }\hbox {C}$$ in Sy I, and from 300 nm at $$1000\,^{\circ }\hbox {C}$$ to 700 nm at $$1200\,^{\circ }\hbox {C}$$ in Sy II. A thermodynamic analysis reveals that the temperature dependence of the characteristic spacing of the symplectite phases is due to a relatively high activation energy for chemical segregation by diffusion within the reaction front as compared to the activation energy for interface reactions at the reaction front. The temperature dependence of the characteristic lamellar spacing and the temperature-time dependence of overall reaction progress have potential for applications in geo-thermometry and geo-speedometry.

The use of metallurgical slags in cement production depends on the phases present in such slags, which are affected by changes in slag composition as well as the cooling rates adopted during solidification. In this work, slags with distinct chemical compositions were melted and subjected to different cooling conditions. Slag samples were characterized by X-ray diffraction to identify and quantify mineralogical phases and by X-ray fluorescence to determine chemical composition. The microstructure of the samples was characterized by scanning electron microscopy coupled to energy dispersive spectroscopy for phase identification. The solidification of the slags was simulated using FactSage™ for solidification path evaluation, enabling a comparison of the phases determined by thermodynamic equilibrium with those analysed in slag samples. Slags with low basicity (CaO/SiO2

A Ghassoul clay from Morocco was studied regarding the effect of (1) grinding and (2) selection of the particle size distribution (classification) on the thermal transformations during sintering. Ghassoul clay contains stevensite, dolomite and quartz as major minerals. Prior to the classification, the starting coarse aggregates of the raw clay were first dry-ground below 500 μm and the obtained particles of powder were then granulated in order to produce adequate pellets for shaping by uniaxial pressing. Classification was performed to obtain three grain size distributions, namely greater than 500 μm, between 500 and 315 μm and lower than 315 μm. As the grain size distribution became finer, the proportion of carbonate phases was increased. DTA–TG analyses were in agreement with this trend, and in addition, dilatometry analyses showed that the densification was shifted to lower temperatures when decreasing the size of granules. The major phases occurring after sintering at 1200 °C were diopside, enstatite and forsterite as expected from the equilibrium phase diagram. Moreover, the smaller clay fraction (typically lower than 40 μm) enhanced the formation of melilite and monticellite. Nevertheless, a swelling occurred during sintering that balanced the densification shrinkage. According to these results, the sintering of Ghassoul clay proceeds through several stages regardless of the particle size selection. With a mean size of granules lower than 315 μm, the densification can be achieved at 1100 °C, while for greater sizes, a similar densification state of the raw material requires a significantly higher temperature of sintering of 1200 °C. In addition, some dedensification drawbacks may occur when using granules whose size is greater than 315 μm and therefore could induce unexpectedly a significant damage to materials. The observed trends may be useful for further applications of such Ghassoul clay in the silicate ceramics field.

Use in ceramic mixes of aluminum-containing waste containing more than 50% Al2O3 facilitates formation of α-Al2O3 and mullite, which improves object physicomechanical and chemical properties. Use of aluminum-containing waste containing less than 30% Al2O3 does not facilitate formation of α-Al2O3 but promotes mullite formation. Cristobalite does not form with use of aluminum-containing waste with an increased amount of alkali (R 2O > 11%), and this has an unfavorable effect on ceramic composite material physicomechanical indices.

Chemical and mineralogical characteristics and physicomechanical properties are provided for mullite-silica refractory MKRA-50 before and after service in a steel-pouring ladle. Questions of metal secondary oxidation present within a lining are considered. A mechanism of sub-compound and gaseous complex formation in steel is discovered and their effect on phase formation in a ladle lining is demonstrated. Thermochemical methods are considered for the preferred choice of refractory materials based on corundum and magnesium oxide.

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.

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.

In the continuous casting of steel, the porous structure of tundish plaster with high-MgO content is commonly used. Destruction of this type of plaster is the result of silicate phases with low melting points that are created when slag containing SiO2 and CaO penetrates into pores of plaster and reacts with periclase (MgO). In this study, two new plasters are developed and their performances in contact with slag are compared with the common plaster by using crucible test. In these new plasters, part of magnesia is replaced by chromite and olivine. Experimental work indicated that basicity gap between slag and plasters is reduced. Destructive reactions between penetrated slag and these new porous plasters are inhibited and phases with high melting points are formed on the surface of primary grains, leading to less dissolution of plasters in slag. This means that the life time of tundish plaster is increased. The reason is that chromite and olivine have less tendency to react with slag rich in SiO2 and probability of formation of destructive silicate phases such as monticellite and merwinite is reduced.

This paper is the second part of a study on recycling magnesite and chromite ore (in the 0–10−3 m fraction) powder, which remains as a production process waste. In this work, 90% magnesite-10% chromite composition was used as a brick composition. Compaction pressure, sintering temperature, ratio of TiO2 addition, and influence of bonding type on refractory properties were examined. In refractory brick production, one of the most important parameters that affects the properties of the product is the particle size distribution of the blend. Experiments show that using a magnesite particle size of −10−3 m and a chromite particle size of −63×10−6 m affects the properties of the product in a positive way. Experiment blends with the particle sizes selected above were used. Magnesite ore was used in experiments after calcination at 1200°C for four hours. In the experiments we mention, MgCl2 and MgSO4 solutions were used as a bonding agent, as a result of which a 6% bonding ratio of MgCl2 and MgSO4 solutions was determined as optimum. The effect of compacting pressure on the refractory properties was studied, and the optimum compacting pressure was determined as 180 MPa. For bricks prepared using calcined magnesite, the optimum sintering temperature was found to be 1750°C. The positive effect of TiO2 addition on the magnesite chrome refractory brick structure has been reported in the literature. Thus, 1, 3, 5, and 7 wt.% TiO2 ratios were used in the blend, and the refractory properties were positively affected by the 3% TiO2 addition. Taking the result of the MgCl2 and MgSO4 bonding solution into consideration, it is clear that the refractory properties of brick can be improved by using a mixture of MgCl2 and MgSO4 bonding solutions. In light of the above concept, bonding mixtures with 1:3, 1:5, and 1:10 ratios were prepared, and these bonding mixtures were studies as a bonding material. The experimental results show that the cold crushing strength (CCS) and volume density of bricks increase, whereas the porosity decreases when a 1:5 ratio of MgCl2 and MgSO4 in the bonding mixture and 3% TiO2 addition were used. Microstructural study of the produced bricks was done using scanning electron microscope (SEM). In addition to this, the phases forming the structure of brick were examined via x-ray diagrams of the material. In bricks where a mixture of a 1:5 MgCl2: MgSO4 bonding solution was used as bonding agent and 3% TiO2 was added, spinel (magnochromite (MgCr2O4)), magnesium orthotitanate (Mg2TiO4), monticellite (CaMgSiO4), and forsterite (Mg2SiO4) phases were found. The perovskite phase was not observed during the experimental study.

Mono-phase ceramics of monticellite (CaMgSiO4) were successfully synthesized by sintering sol-gel-derived monticellite powder compacts at 1,480 degrees C for 6 h. The mechanical properties and the coefficient of thermal expansion (CTE) of the monticellite ceramics were tested. In addition, the bioactivity in vitro of the monticellite ceramics was evaluated by investigating their bone-like apatite-formation ability in simulated body fluid (SBF), and the biocompatibility in vitro was detected by osteoblast adhesion and proliferation assay. The results showed that the bending strength, fracture toughness and Young's modulus of the monticellite ceramics were about 159.7 MPa, 1.63 MPa m1/2 and 51 GPa, respectively. The CTE was 10.76x10(-6) degrees C(-1) and close to that of Ti-6Al-4V alloy (10.03x10(-6) degrees C(-1)). Furthermore, the monticellite ceramics possessed bone-like apatite-formation ability in SBF and could release soluble ionic products to significantly stimulate cell growth and proliferation. In addition, osteoblasts adhered and spread well on the monticellite ceramics, which indicated good bioactivity and biocompatibility.

This study concerns the chemical reactions involved and the phases formed during penetration of slags of variable composition into porous plaster structure of tundish. Tundish plaster is mainly composed of MgO with minor amounts of SiO2 and impurities, with a grain size of less than 1 mm, inorganic or organic fibers in order to decrease density and provide porosity for insulation, plasticizers and stiffening agents and some other additions. Tundish slag analysis for different grades of steel (7176D and 1191D, according to DIN standard) at different sequences, indicated a very variable composition of CaO (11–42%), SiO2 (28–46%), Al2O3 (6–12%), MgO (11–20%), MnO (0–13%) and some minor variations of Fe, FeO and TiO2. Experimental work indicated that slag when penetrated into pores of plaster, develop the phases of Monticellite (CaO · MgO · SiO2) and Merwinite (CaO1.5 · MgO0.5 · SiO2) around MgO particles and decrease the liquidus temperature from 2,800 °C to about 1,500 °C and provide dissolution of MgO grains in steel making process. Calculation based on two kinetic equations developed for diffusion controlled dissolution, indicated that the dissolution of MgO in tundish plaster is not a diffusion controlled process and is affected by turbulent flow parameters. Phase diagram of CaO–SiO2–MgO indicates that decreasing SiO2 to below 20% and increasing CaO content to as high as possible, increases the liquidus temperature to above 2,000 °C. Sources of SiO2 in the process are the rice husk addition, which is used as an insulating material on top of the melt, and the slag flux addition. These sources should be reduced to as low a level as possible. This fact does not affect the fluidity of slag which is required for inclusion removal. Fluidity of slag comes from low melting point eutectics in CaO–Fe2O3 and CaO–FeO (about 1,200 °C) due to iron oxide on top of the steel melt.

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.

The resistance of magnesian spinellide refractories to molten slag attack is studied and effects associated with the material composition and the microstructure of test specimens are discussed. The mechanisms of corrosion wear and chemical reactions involved are considered in detail. Slags with a basicity of 1.9 – 2.1 react with periclase to yield spinel, calcium orthosilicate, and monticellite. To prevent the chemical corrosion of periclase, sintered periclase or alumina as additions to the slag are recommended for use.

X-ray phase and electron-microscopic methods showed that wollastonite and anortite determine the strength of ceramic facings of the Shakhi-Zinda ensemble. In addition, the isometric pores and oval closed porosity present in the ceramic facing of the Shakhi-Zinda ensemble increase durability.

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.

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.

Polarized single-crystal infrared (IR) reflectance spectra measured for synthetic fayalite (Fe2SiO4) possess all but one of the peaks mandated by symmetry plus a few weak bands attributable to overtones. Fayalite has a band at 86 cm−1, which is below the frequency range commonly examined, suggesting that vibrational spectra of ferrous minerals may need remeasuring. B2u polarizations were also measured for natural monticellite (nearly MgCaSiO4) and synthetic Mg2Si18O4. Thin film absorption data were collected for the above species, Co2SiO4, Mn2SiO4, Mg2SiO4, (Mg1.9Fe0.1)SiO4, Mg2GeO4 and Mn2GeO4. The relationships of IR peak positions (from these data and from previous single-crystal studies) with the inverse square root of the average cation mass were used to make band assignments, to estimate the positions for missing bands, and to determine which peaks are degenerate. The pressure dependencies of monticellite IR peaks were measured and resemble those of other olivines.

Bulk compositions and mineral analyses for forty-one, large, garnet- and spinel-facies peridotite xenoliths from the Udachnaya kimberlite in the central Siberian platform have many similarities to those of well-studied peridotites from the Kaapvaal craton in southern Africa. Coarse Mg-rich lherzolites and harzburgites with equilibration temperatures below 1000 °C are abundant and are believed to form the principal rock type in the Siberian lithosphere. The low-temperature Udachnaya peridotites have an average mg number [Mg/(Mg+Fe)] of 92.6 with a wide dispersion in modal enstatite, ranging to over 40 wt%. High-temperature peridotites are relatively richer in Fe and Ti and are commonly deformed, with porphyroclastic or mosaic-porphyroclastic textures, some of the latter having fluidized enstatite. The Udachnaya peridotites have experienced late-stage metasomatism before, during and after eruption. Garnets and pyroxenes in many of the high-temperature rocks are zoned, probably by reaction with melt prior to eruption. Virtually all the peridotites contain secondary diopside, inhomogeneous on a micron scale, that mantles primary orthopyroxene. It is believed to have crystallized along with lesser amounts of intergranular calcite and monticellite during eruption. Bulk analyses for total Fe in many specimens are higher than whole-rock Fe calculated from the electron probe analyses and the modes. The magnitude of the difference between the two measurements of total Fe correlates with loss-on-ignition, suggesting that Fe has been introduced during serpentinization following eruption. These late metasomatic processes have thus affected some major as well minor and trace element compositions. The similarities in bulk composition of peridotites from Udachnaya and the Kaapvaal are evidence of a common origin. Low-temperature cratonic peridotites differ from oceanic peridotites in having higher mg numbers (>92) and in having relatively high but wide-ranging modal enstatite (Mg/Si = 1.06–1.49 weight fraction). The Udachnaya low-temperature peridotites have an inverse correlation between FeO (calculated from the probe analyses and modes) and SiO2. This correlation is also present in the Kaapvaal data but is complicated by a greater range in fertility that produces a positive variation of Fe with Si. A negative trend for Fe/Si can be seen within a portion of the Kaapvaal data, that for low-Ca harzburgites, in which the variation in fertility is restricted. The negative trends for Fe/Si can be interpreted as a consequence of either segregation of olivine and orthopyroxene by metamorphic differentiation or partial sorting during cumulate formation.

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.

A study was made of the physical-technical properties of granules obtained from magnesia-silicate natural raw materials by a process involving blowing the fusions. A relationship was identified between the structure and phase composition of the granules and the composition of the original raw materials.

Phase fields intersected by three joins in the System CaO-MgO-SiO_2-CO_2-H_2O at 2 kbar were investigated experimentally to determine the melting relationships and the sequences of crystallization of liquids co-precipitating silicate minerals and carbonates. These joins connect SiO_2 to three mixtures of CaCO_3-MgCO_3-Mg(OH)_2 with compositions on the primary field for calcite, between the composition CaCO_3 and the low-temperature (650°C eutectic liquid co-precipitating calcite, dolomite and periclase. In the pseudo-quaternary tetrahedron calcite-magnesite-brucite-diopside, two of the significant reactions found are: (1) a eutectic at 650°C, calcite + dolomite + periclase + forsterite + vapor = liquid, and (2) a peritectic at 1038°C which is either calcite + akermanite + forsterite + vapor = monticellite + liquid calcite + monticellite + forsterite + vapor = akermanite + liquid. The eutectic liquid has high MgO/CaO and CO_2/H_2O and only 2–3% SiO_2 (estimated 15–20% MgCO_3, 35–40% CaCO_3, 40–45% Mg(OH)_2, and 5–6% Mg_2SiO_4). The composition joins intersect a thermal maximum for akermanite + forsterite + vapor = liquid, which separates high-temperature liquids precipitating silicates together with a little calcite, from low-temperature liquids precipitating carbonates with a few percent of forsterite; there is no direct path between the silicate and synthetic carbonatite liquids on these joins, but it is possible that fractionating liquid paths diverging from the joins may connect them. More complex relationships involving the precipitation of monticellite and akermanite are also outlined. Magnetite-magnesioferrite may replace periclase in natural magmatic systems. The results indicate that the assemblage calcite-dolomite-magnetite-forsterite represents the closing stages of crystallization of carbonatites, whereas assemblages such as calcite-magnetite-forsterite and dolomite-magnetite-forsterite span the whole range of carbonatite evolution in terms of temperature and composition, and provide the link between liquids precipitating silicates and those precipitating carbonates.

Two small diatremes, about 0.25 my old, cut through Liassic limestones about 1 km NNE of the village of Polino (Long. 12°50'54″E-Lat. 42°35'34″N; Central Italy). The material filling the larger diatreme is mainly composed of a tuffisite with abundant lapilli showing concentric structure. Both unaltered country-rocks and massive hypabyssal carbonatite occur in the tuffisite as angular clasts and blocks, from a few mm up to more than 1 m in diameter. The Polino rock occurs in a strongly-potassic igneous district (Umbria Latium Ultra-alkaline District) which comprises phonolitic pyroclastic rocks and very rare kamafugitic lavas. Massive carbonatite blocks have an average mode of 53% Sr-Ba-rich calcite, 23% Fe-monticellite, 9% Th-perovskite plus Ti-magnetite, 6% Cr-phlogopite, 6% forsteritic olivine, about 2% Zr-schorlomite and ca. 1% Si-CO-OH apatite. Perovskite, schorlom ite, and apatite form cognate phases, whereas olivine and phlogopite, often replaced by monticellite, occur as nodules and as discrete grains with compositions and deformation features typical of mantle xenocrysts found in alkali basalts and ultramafic rocks. High modal content of Ca-carbonate, high Sr, Ba and LREE contents of calcite, the presence of rare minerals peculiar to carbonatitic rocks and an essential amount of monticellite indicate classification of the Polino rock as a monticellite calciocarbonatite. The Polino rock represents a carbonatitic melt strongly contaminated by mantle-crystal debris. It displays unusual geochemical features having trace elements closer to those of the regional-associated kamafugitic rocks rather than to those of common carbonatites.

The stability of merwinite (Mw) and its equivalent assemblages, akermanite (Ak)+calcite (Cc), diopside (Di)+calcite, and wollastonite (Wo)+monticellite (Mc)+calcite was determined at T=500–900° C and Pf=0.5–2.0 kbar under H2O−CO2 fluid conditions with XCO2=0.5, 0.1, 0.05, and 0.02. Merwinite is stable at Pf=0.5 kbar with T>700° C and XCO2

A detailed petrological study of the S. Venanzo olivine melilitite and Cupaello kalsilitite, located at the NE margin of the Roman Comagmatic Region of Italy has provided new data to evaluate their genetic relationships and related tectonic/magmatic conditions. Early crystallized olivine (Fo92) from S. Venanzo is compatible with crystallization from near primary mantle melts, while late-crystallized olivine from both rocks (Fo88–79) reflects primarily the high Ca of the host liquids, attained under the volcanic crystallization regime. Magnesiochromite inclusions in the early-crystallized olivine are consistent with near-primary melts close to lamproite in composition. Nepheline and kalsilite from both lavas contain high alkalis (+Ca), relative to Al, and thus correspond more closely with nepheline compositions from carbonatite-related assemblages, than with those from a wide compositional range of Alban Hills lavas. Coexisting melilite has high (Na+K)/Al, reflecting the Peralkalinity Index of the bulk rocks. Diopside and phlogopite from both lavas are characteristic of lamproites and groundmass kimberlites in their high Mg/(Mg+Fe2+) ratio (0.86–0.95; 0.80–0.90, respectively) and T-site (Si+Al) deficiencies. Gotzenite, Ca2Na[Zr, Ti]Si2O7(O, OH, F)2, identified in both lavas, is typical of nephelinite-ijolite assemblages. On the other hand, khibinskite, K4Zr2Si4O14, found in the Cupaello lava, may be regarded as a Si-poor variety of wadeite, a mineral characteristic of lamproites. Clinopyroxene and monticellite, coexisting as late-crystallized phases in both lavas, suggest a common P-T liquid path of thermal descent in the system CaMgSi2O7−CO2 in the presence of excess CO2, but with different intersections with the akermanite stability field. Substantial differences in SiO2 saturation combined with high Mg number and liquidus temperatures experimentally determined at atmospheric pressure in both lavas (1276° C and 1260° C, respectively) indicate that a parent-daughter relationship is unlikely under the volcanic P-T regime. In La Roche's “Rm-Ri-Rs” diagram, the S. Venanzo composition fall close to the Oldoinyo Lengai alkalic pyroxenite trend of Donaldson and Dawson, while the Cupaello compositions follow a lamproitic trend, consistent with that indicated by the quartz-normative glass of the Gaussberg lava. Mantle compositions corresponding to wehrlite-clinopyroxenite and enriched in H2O, CO2, F, and LILE, are favoured as potential sources for the lavas. Their origin is probably related to subcrustal fluid transfer promoted by the Tyrrhenian mantle doming.

Ion microprobe analysis of magnetites from the Adirondack Mountains, NY, yields oxygen isotope ratios with spatial resolution of 2–8 μm and precision in the range of 1‰ (1 sigma). These analyses represent 11 orders of magnitude reduction in sample size compared to conventional analyses on this material and they are the first report of routinely reproducible precision in the 1 per mil range for analysis of δ18O at this scale. High precision micro-analyses of this sort will permit wide-ranging new applications in stable isotope geochemistry. The analyzed magnetites form nearly spherical grains in a calcite matrix with diopside and monticellite. Textures are characteristic of granulite facies marbles and show no evidence for retrograde recrystallization of magnetite. Magnetites are near to Fe3O4 in composition, and optically and chemically homogeneous. A combination of ion probe plus conventional BrF5 analysis shows that individual grains are homogeneous with δ18O=8.9±1‰ SMOW from the core to near the rim of 0.1–1.2 mm diameter grains. Depth profiling into crystal growth faces of magnetites shows that rims are 9‰ depleted in δ18O. These low δ18O values increase in smooth gradients across the outer 10 μm of magnetite rims in contact with calcite. These are the sharpest intracrystalline gradients measured to date in geological materials. This discovery is confirmed by bulk analysis of 150–350 μm diameter magnetites which average 1.2‰ lower in δ18O than coarse magnetites due to low δ18O rims. Conventional analysis of coexisting calcite yields °18O=18.19, suggesting that bulk Δ18O (Cc-Mt)=9.3‰ and yielding an apparent equilibration “temperature” of 525° C, over 200° C below the temperature of regional metamorphism. Consideration of experimental diffusion data and grain size distribution for magnetite and calcite suggests two contrasting cooling histories. The data for oxygen in calcite under hydrothermal conditions at high P(H2O) indicates that diffusion is faster in magnetite and modelling of the low δ18O rims on magnetite would suggest that the Adirondacks experienced slow cooling after Grenville metamorphism, followed by a brief period of rapid cooling, possibly related to uplift. Conversely, the data for calcite at low P(H2O) show slower oxygen diffusion than in magnetite. Modelling based on these data is consistent with geochronology that shows slow cooling through the blocking temperature of both minerals, suggesting that the low δ18O rims form by exchange with late, low temperature fluids similar to those that infiltrated the rock to serpentinize monticellite and which infiltrated adjacent anorthosite to form late calcite veinlets. In either case, the ion microprobe results indicate that two distinct events are recorded in the post-metamorphic exchange history of these magnetites. Recognition of these events is only possible through microanalysis and has important implications for geothermometry.

Full-scale tests of pilot batches of periclase-spinel-carbon articles of grade PShUS-2 produced by the Dinur Company in the lining of the tank of an IChKM-10-Sl mixer operating at the Sinarskii Pipe Plant are described. The effectiveness of the use of the tested refractories is 2.5-3.0 times higher than that of corundum articles of grades KSP and KF. The endurance of the refractories is determined by the rate of oxidation of carbon.

Interfaces between glass and crystalline grains have been examined using a thin-film geometry which allows the use of newly developed experimental methods for micromechanical testing of interfaces. In this approach, continuous films of thicknesses ranging 100–200 nm of anorthite (CaAl2Si2O8), celsian (BaAl2Si2O8), and monticellite (CaMgSiO4) are deposited onto single-crystal Al2O3 (α-structure) surfaces of different crystallographic orientations by pulsed-laser deposition (PLD).Mechanical properties such as hardness, stiffness, and reduced Young's modulus were probed with a newly developed high-resolution depth-sensing indentation instrument. Emphasis has been placed on examining how changes in the glass composition will affect the mechanical properties of the single-crystal Al2O3/silicate-glass interfaces. The indentation data obtained from these experiments correlate directly to the morphology of the deformed regions imaged with atomic force microscopy (AFM). Nanomechanical tests combined with AFM imaging of the deformed regions allow force-displacement measurements and in-situ imaging of the same regions of the specimen before and immediately after indentation. This new technique eliminates the uncertainty of locating the indenter after unloading.

Thin, calcium magnesium silicate glass films have been deposited onto (001) -oriented single-crystal MgO substrates by pulsed-laser deposition (PLD). The substrates were thinned to electron transparency and characterized in the transmission electron Microscope (TEM) before and after the deposition and following different heat treatments. Energy Dispersive X-ray Spectroscopy (EDS) was used in the TEM to characterize the chemistry of the films. The heat treatments were performed both in situ and ex situ. Direct evidence for crystallization was obtained by in-situ experiments at 950°C. Subsequent heat treatments were performed for longer times in air between 950°C and 1100°C. The crystallized phase was found to be Monticellite (CaMgSiO4) and the crystallites show moderate epitaxy with the underlying substrate. Films contaminated with aluminum resulted in the growth of magnesium aluminate spinel (MgAl2O4) epitaxially from the substrate. These observations of epitaxy indicated that crystallization initiated at the surface of MgO.

The adiabatic single-crystal elastic moduli of a natural sample of monticellite (CaMgSiO4), with the olivine crystal structure, have been measured under ambient conditions using Brillouin spectroscopy. From the single-crystal moduli the aggregate bulk and shear moduli are calculated to be Ks=106±1 and μ = 55.2±0.4 GPa, respectively. These results are consistent with a systematic decrease in bulk modulus with increasing molar volume among the olivine-structured silicates. The longitudinal moduli decrease in the order c11>c33>c22, indicating that the structure is stiffest along the a axis and most compliant along the b axis. This relationship among the longitudinal moduli holds for all silicate and germanate olivines, and is thus inferred to result from the topology of the olivine crystal structure. However, the moduli obtained in this study are at variance with previous conclusions concerning deviations from the Cauchy relations (e.g. c12=c44). For monticellite, off-diagonal shear moduli of the c12-type are uniformly greater than pure shear moduli such as c44. Similar behavior is found in pyroxenes such as diopside. The relative magnitudes of shear and off-diagonal moduli are not, therefore, a diagnostic chemical signature in minerals with complex crystal structures.

One atmosphere liquid-present experiments were carried out in the CMAS system using an ordinary quench furnace apparatus. The runs, including reversal and duplicate experiments, describe the univariant curve l=fo+an+ di between the invariant points Q: l+fo+an=di+sp and F: l+fo=an+di+oen, located respectively at 1245±1° C and 1244±1° C. The thermal divide on this curve M3: l= fo+an+di is located at 1275±1° C and plots well within the silica-saturated field, in agreement with Longhi's (1987) experiments. Along the univariant curve l=fo+an+di, liquid composition evolves away from the thermal divide either toward invariant points Q or F and pierces the silica saturation plane, i.e., the join Di-An-En, in the silica saturated field. In this compositional range, the Al solubility in clinopyroxene changes drastically from one side of the thermal divide to the other, with great increase of Al solubility in the silica-undersaturated field. Four endmembers must be used to describe the complex solid solution of anorthite: CaAl2Si2O8, CaMgSi3O8, MgAl2Si2O8 and [] Si4O8. The last two of these are present only within the silica-saturated field. Unlike clinopyroxene, the Mg content of anorthite is insensitive to the thermal barrier but is only sensitive to silica-saturation plane. Olivine composition can be described by a binary solid solution of forsterite and monticellite with no Ca in the M2 site. As with anorthite, olivine compositions exhibit a marked change with crossing of the silica-saturation plane. The above features imply that the solubility of minor elements in crystalline phases (Al in clinopyroxene, Ca in olivine and Mg in anorthite) selectively respond to only one or another of these particular plane. Results have many important consequences. One is the likelihood of changes in melt speciation depending on position with respect to the thermal divide and the silica-saturation plane.

The most durable batcher inserts for casting low-carbon rimming steels are those produced from periclase processed from powders containing a minimum of impurities, i.e., 3% or less. A small proportion of monticellite (up to 2.5%) in the periclase product does not affect durability adversely to an appreciable extent. A combination of monticellite with other impurity phases (magnesioferrite, forsterite) to an aggregate proportion of 8–9% greatly reduces the durability of the insert in steelcasting. It was established that dicalcium silicate also has an adverse effect.

The article describes the thermal metamorphism of siliceous carbonate rocks near the dolerite intrusive body in Eastern Siberia. The mineral associations at the immediate contact with dolerite are the following: wollastonite+rankinite, rankinite+spurrite (+melilite?), spurrite+melilite+merwinite+calcite and merwinite+monticellite+melilite+calcite. The melilite in these associations is usually unzoned; its composition being essentially gehlenitic. During the regressive stage of contact metamorphism new akermanite-rich melilite and calcite were formed by replacement of merwinite and earlier gehlenitic melilite through participation of CO2. The newly forming melilite grains have sharp compositional zoning. The origin of zoning was connected with the fall of temperature and decrease of the mole fraction of CO2 in the fluid equilibrated with the minerals.

A detailed isotopic study of minerals and whole rocks from the Cretaceous Oka complex, Quebec, Canada, shows a very small variation in initial Nd and Sr isotopic compositions. Assuming an age of 109 Ma for the complex, apatite, calcite, garnet, melilite, monticellite, olivine and pyroxene and whole rocks yield a range for initial 87Sr/86Sr of 0.70323–0.70333; and for initial 143Nd/144Nd of 0.51271–0.51284 (eSR(T)= −14.8 to −16.2; eNd(T)=+4.1 to +6.6). The negative eSR and positive eNd indicate derivation of the Nd and Sr from a source with a time-integrated depletion in the large-ion lithophile (LIL) elements. This agrees with data from other Canadian carbonatites and confirms that a large part of the Canadian Shield is underlain by a source region depleted in the LIL elements. The new data from Oka suggest that the depleted source may have remained coupled to the continental crust until recent time.

Calcium-olivine, γ-Ca2SiO4, larnite, β-Ca2SiO4, merwinite, Ca3Mg(SiO4)2, and monticellite, CaMgSiO4, are considered. According to a rigid oxyanion scheme, eulerian orientation angles of the SiO4 tetrahedra and translation coordinates of Ca and Si atoms are specified as structural variables τk. All derivatives of the static energy (Born model) contain atomic charges and repulsive parameters as unknowns; the minimum energy conditions ∂E L/∂τk=0 yield 34 equations which are solved by a least-squares method. The set of energy parameters fitting structural properties of all four phases together is: z Ca=1.50, z o=−1.10 e, r Ca=1.05, ρ=0.25 A; the Mg charge was fixed at 1.38 e, from a previous study on forsterite. An average shift of 0.04 A is observed between experimental and least-energy calculated atomic positions. Results are compared with those of Mg2SiO4, where the fit was based both on thermoelastic and on structural properties. If no charge values were fixed “a priori”, just ratios between charges could be determined by fitting them to structural data only.

Akermanite (Ak90) coexists with monticellite (Mo92) and wollastonite (Wo99) in an unusual calc-silicate xenolith in anorthosite at Cascade Slide in the Adirondack Mountains, New York. Experimental results bearing on the stability of akermanite have been evaluated through calculations based on thermochemical data and by chemical analysis of experimental products (Yoder 1975). A temperature of 750°±30° C and a pressure less than 7 kb are inferred. These estimates are in agreement with the conditions of regional metamorphism previously inferred from other nearby rock types. When errors are considered, all existing data show that the Cascade Slide mineral assemblages last equilibrated at a slightly higher pressure of 7.4±1 kb and at a temperature of 750°±30° C during regional granulite facies metamorphism. The exotic mineralogy at Cascade Slide (akermanite, monticellite, cuspidine and wilkeite) was stabilized by low carbon dioxide fugacity. Posttectonic anorthosite intrusion is ruled out by the absence of a preserved contact aureole.

The carbonatite at Magnet Cove, Arkansas, USA contains a great variety and abundance of magmatic and hydrothermal inclusions that provide an informative, though fragmentary, record of the original carbonatite melt and of late hydrothermal solutions which permeated the complex in postmagmatic time. These inclusions were studied by optical and scanning electron microscopy.

In metallurgical magnesite (periclase) powder obtained in rotary kilns of length 50, 75, 90, and 170 m one encounters no less than eight structural genetic types of granules (fusions) in which are selectively concentrated the impurities CaO, SiO2, etc. The commonest are diabase and dolomite granules. The formation of diabase and clayey (aluminous) fusions is due to the cementation of periclase particles by the melts, formed deposited from the mechanical impurities in the raw material. Morphologically and genetically similar chamotte, and frequently ferruginous, fusions develop as a result of the granulation of aggregate periclase grains of fusible products from the breaking up of the lining in the rotary kilns. The formation of dolomite and diabase-dolomite fusions with an internal core from the products of the decomposition of the broken primary dolomite is connected with the power of the latter to be preserved during firing in the form of lumps, and not subjected (in contrast to magnesite) to self-dispersion. In the formation of granules chemical reactions occur between the periclase, lime, and molten fusible impurities in the magnesite raw materials. The products of the reaction are spinel, magnesioferrite, forsterite, monticellite, merwinite, cordierite, and silicates and ferrites of calcium. In connection with the increase in the concentration of fusible impurities the fusions (granules) are poor quality constitutents of the magnesite powder.

After current and capital repairs, the basic phase in the hearths is periclase. Apart from periclase there is also magnesioferrite, monticellite and forsterite.

Converter slags formed in the first 10–12 min of the blowing of the iron, after cooling consist mainly of manganese-iron monticellite, glassy, and cryptocrystalline substances, free calcium oxide, and metallic iron. The primary slags are characterized by a low basicity, refractoriness, and viscosity, and rapidly react with the refractory during the period of their formation in the converter at 1150–1360°C. The primary slags are changed into the truly liquid state at 1256–1312°C.

The life of the lining of arc furnaces is determined by the grade of steel being melted. When stainless steels are being melted, the life of the lining in a 40-ton furnace is 20% higher than when melting ball-bearing steels and transformer steels; in 10-ton furnaces the life is 3.5–3.7 times higher than when melting constructional steels. The high life of linings when melting stainless steels is due to the formation of a chromic crust, fulfilling the role of working layer of the lining which is restored at each melt on account of the chrome-titania slags of the oxidation period of the melt. In mineral composition the crust consists of highly refractory spinel of complex composition (70–80%) the interspaces between the grains of which are filled with manganous monticellite and glass (up to 20–30%). When melting other steels, the crust on the lining is not formed, and contact with the slag leads to a high erosion rate.