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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.

The exchange reaction of Fe2+ and Mg2+ between olivine and clinopyroxene has been experimentally determined at 1150°C, and at pressures 1 and 1. 5 GPa in the Ca-poor and Ca-enriched systems, the bulk ratio Fe/ (Fe+Mg) which was fixed as about 0. 5. The CaO contents of olivine and clinopyroxene seriously affect on the Fe-Mg partition coefficient KD [= (XCpxMg XOlFe) / (XCpxFe XOlMg) ], which increases with increasing XOlCa. The KD was found as 1. 50 at 1 GPa for the assemblage of olivine (XOlCa = 0. 006) and subcalcic clinopyroxene (XCpxCa = 0. 2898) ; 2. 90 at 1. 5 GPa for the assemblage of diopside-hedenbergite clinopyroxene and olivine (XOlCa = 0. 1048), in contrast to 3. 00 at 1 GPa for the assemblage of diopside-hedenbergite clinopyroxene, olivine with XOlCa = 0. 1464 and ferroan monticellite. On the other hand, the distribution coefficient KD was found to be insensitive to pressure comparing with the previous data. The olivine-ferroan monticellite solvus becomes narrow with increasing pressure, but this pressure effect on the solvus is very small.

Mg and Fe $K$-edge x-ray absorption near-edge spectroscopy spectra of the $\mathrm{Pbnm}$ olivine series end members forsterite, fayalite, monticellite, and kirschsteinite, as well as of a synthetic Fe-Mg olivine of intermediate composition (Fo50), have been recorded and compared with multiple-scattering simulations. A comparison of experimental and theoretical spectra shows that all transition features, energy positions, and relative intensities can be reproduced in the energy range up to 60 eV above threshold when using clusters containing at least 80 atoms and extending over a sphere at least 0.6 nm in radius away from the absorber. Mg and Fe are entirely in the expected structural sites in the four investigated end members. None of the models of Mg and Fe ordering in the octahedral site for the Fe50 olivine compound proposed so far is verified; thus Fe-Mg ordering still remains an open problem for olivines of intermediate compositions.

Almost monomineralic Mg-rich gehlenite (similar toGh(50)Ak(46)Na-mel(4)) skarns occur in a very restricted area along the contact of a diorite intrusion at Oravita, Banat, in Romania, elsewhere characterized by more typical vesuvianite-garnet skarns. In the vein-like body of apparently unaltered gehlenite, the textural relations of the associated minerals (interstitial granditic garnet and, locally, monticellite, rare cases of exsolution of magnetite in the core zone of melilite grains) suggest that the original composition of the gehlenite may have been different, richer in Si, Mg, Fe (and perhaps Na), in accordance with the fact that skarns are the only terrestrial type of occurrence of gehlenite-dominant melilite. The same minerals, monticellite and a granditic garnet, appear in the retrograde evolution of the Mg-rich gehlenite toward compositions richer in Al, the successive stages of which are clearly displayed, along with the final transformation to vesuvianite. These changes include (1) the local development of small rounded patches with Al-rich compositions (Gh(60) to Gh(85)), accompanied by monticellite, spurrite (or tilleyite, afwillite, kilchoanite) and, at a later stage, a granditic garnet, and (2) the complete transformation of gehlenite to vesuvianite, associated with minor clintonite (+ monticellite and probably ellestadite), usually along a sharp front typically rimmed by a 0.5-mm-wide zone of Al-rich gehlenite (Gh(85)). The gehlenite rim, as well as the gehlenite in the local modifications, show a remarkable correlation between the akermanite and Na-melilite contents, probably of crystal-chemical origin. The local modifications (1) are interpreted as nearly closed-system (except for Na and Fe) retrograde reactions at moderate temperature (500-600degreesC), controlled by the localized presence of small amounts of fluid at low pressure, mainly involving the transformation of the akermanite component to monticellite. The silica released by this transformation resulted in the formation of spurrite (among others) and of the Na-melilite component at first, and garnet later. The subsequent transformation (2) of geldenite to vesuvianite and clintonite, which involved silica metasomatism, may result from the more pervasive infiltration of the same fluid, at higher pressure, probably related to the development of the garnet-vesuvianite skarns elsewhere along the intrusive contacts.

Mesozoic melilite-bearing ultramafic lamprophyres are developed as sill, dyke and plug-like intrusive bodies in the East Antarctic Beaver Lake area. They consist of varying amounts of olivine, melilite, phlogopite, nepheline, titanomagnetite and perovskite as major phases, accompanied by minor amounts of apatite, carbonate, spinel, glass and, rarely, monticellite. The rocks are mineralogically and geochemically broadly similar to olivine melilitites, differing in higher CO2 and modal phlogopite and carbonate contents. The ultramafic lamprophyres are MgO-rich (13.4–20.5 wt%) and SiO2-poor (32.8–37.2 wt%), indicative of a near-primary nature. Major and trace element features are consistent with minor fractionation of olivine and Cr-spinel from melts originating at depths of 130–140 km.

In order to reduce B2O3 content in sintered magnesium oxide as much as possible, in precipitation with 80 percentage of the stoichiometric quantity of dolomite lime, the effect of the pH of the agent used for rinsing the magnesium hydroxide precipitate was examined, as well as the effect of mannitol in sea water before precipitation. Mannitol binds orthoboric acid present in sea water into a weakly dissociated complex acid HB(OC)4. Experiments have shown that the B2O3 content in sintered magnesium oxide samples is satisfactorily low. The lowest B2O3 content is obtained when mannitol is added ; no B2O3 was found in these samples after sintering. Magnesium oxide samples were sintered at 1500oC ; duration of isothermal sintering was one hour. Values for density and porosity of individually sintered samples are listed. The ratio CaO/SiO2 indicates that forsterite (Mg2SiO4), monticellite (CaMgSiO4) and mervinite (Ca3MgSi2O8) are formed during sintering of the samples.

Olivines from igneous rocks generally have low calcium contents. However, olivines crystallized from strongly silica-undersaturated magmas occasionally contain large amounts of kirschsteinite (Ki" CaFeSiO4) and monticellite (Mo: CaMgSiO4) components. The purpose of this note is to report the first natural occurrence of kirschsteinite crystals that have lamite (La: CazSiO4) in the mineralogical norm.

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.

The recent years have witnessed an unprecedented growth in the development and deployment of electromagnetic field(EMF) used in steel metallurgy. This paper investigates the effect of EMF on the slag resistance of MgO-C refractories. Using MgO-C refractories containing 14% carbon and the slag with a basicity(CaO/SiO2) of around 0.8, the experiments of melting slag resistance of MgO-C refractories were carried out in an induction furnace and a resistance furnace. The results show that in induction furnace having EMF, the refractory sample corroded by the slag has an apparent penetration layer. MgFe2O4 phase is formed at a low temperature by MgO dissolved in Fe2O3. The low melting phases are monticellite (CaMgSiO4, CMS) and forsterite (Mg2SiO4, MS). Under the condition of resistance furnace without EMF, scaling MgO dissolves into slag and reacts with Al2O3 to generate MgAl2O4 phase. The low melting phases are gehlenite (Ca2Al2SiO7, C2A2S) and akermanite (Ca2MgSi2O, C2MS2). As EMF exists at a high temperature, it could enhance the diffusion and penetration of Fe2+/3+ ions to form the MgFe2O4 phase. At the same time, some MgAl2O4 spinels exist. However, only MgAl2O4 phase can be generated without EMF.

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.

Silicate glasses are the most common constituents of intergranular phases which can be found in liquid-phase sintered ceramics [1]. Silicates are known to influence the structure of ceramic interfaces which, in turn, frequently affect mechanical properties of ceramic materials [2]. In earlier studies of silicate glasses on single-crystal alumina Ramamurthy et al [3] and Mallamaci [4] showed that the morphology of dewetted glass films and the mechanism of devitrification depend on the crystallographic orientation of the substrate surface. In continuation of these studies, results are presented on the dewetting behavior of monticellite (CaMgSi04) in contact with the (OOl)-oriented surface of single-crystal MgO. Due to the simplicity of sample preparation and availability of 3- dimensional topographic information, Atomic Force Microscopy (AFM) was used for surface characterization. These AFM results are complemented by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) data on the chemical composition and the structure of the glass-substrate interface.

Interrelationships among the chemical formulae of over 20 common silicate minerals are revealed in a diagram in which six radial axes centered on quartz terminate in the minerals nepheline, kalsilite, kyanite, forsterite, monticellite, and larnite. In addition to its mnemonic value, the diagram is a pedagogic aid in grouping silicate structures and in revealing which mineral assemblages may coexist in equilibrium.

Magnesioferrite, monticellite, perovskite and calcium brittle mica occur in the alpine-type Iwanai-dake peridotite mass in the Kamuikotan structural belt, Hokkaido. These minerals were not primary phases, but were produced through metasomatic processes at a later stage of the granulite facies equilibration.

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.

Hydrothermal treatment of albite, labradorite, and orthoclase in mixtures with dolomite has revealed that at PH2O = 1000 kg/cm2 and a residence time of 24-72 hr at T = 200–400° C, mainly calcite and trioctahedral layered silicates are formed. At 300–500° we observe the following formation sequence: montmorillonite → (Mg, Al) serpentine → chlorite from plagioclases and montmorillonite → a disordered mixed-layer phase of the mica-montmorillonite type → phlogopite from orthoclase. At 500–600° there is a tendency for formation of framework aluminosilicates (nepheline, kalsilite) at high Na and K concentrations in the initial mixtures, and nesosilicates (monticellite, forsterite) at high Ca and Mg concentrations. It is shown that as the residence time is increased synthetic and natural montmorillonites with AlIV are not converted to ordered 1:1 mixed-layer phases, in contrast to those observed in systems with kaolinite. This is probably due to the statistically uniform distribution of A1 in a structure of beid...

FT-IR and Raman spectra in room and liquid N 2 temperature have been recorded for the isotopic species of the monticellite. The band assignments have been deduced from 24 Mg – 26 Mg, 40 Ca – 44 Ca and 28 Si – 30 Si isotopic shifts. Based on these data isotopically adjusted GVFF force constants have been calculated with different models (unit cell, isolated SiO 4 anion with C point symmetry). Force constants for izomorphic Mg 2 SiO 4 and α-C s a 2 SiO 4 structures have been also obtained.

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.

Carbonatite from Magnet Cove, Arkansas, was crushed, minerals hand-picked to obtain pure separates, and then analyzed for U content by delayed-neutron activation analysis (DNAA). Most minerals exhibited U values within their usual range in silicate rocks. These include magnetite, pyrite and apatite. Calcite contains slightly more U than average limestone; monticellite averages 2.16 ppm U. Only in perovskite and the CaZrTi-garnet kimzeyite is U quite high at ∼ 200 ppm. The high U values in the latter two minerals are due to the ability of U (IV) to substitute for Ti in the perovskite, and for Zr and Ti in the garnet.

The effects of silicate boundary phase provided by monticellite (CaMgSiO4) decomposition in situ on the sintering behaviour of magnesium oxide powder compacts have been studied. The parameteis include median particle size, nature and quantity of silicate liquids and thermal treatments.Inadequate amount of viscous liquid formation at 1490°C due to peritectic reaction of monticellite (CMS) seemed to hinder the densificaron in magnesia-monticellite system. On the other hand, complete melting of monticellite at 1650°C enhanced densification to 3.16 gm.cm−3 from 2.75 gm.cm −3 at 1490°C for samples containing 12% CMS. Under the conditions of sintering, liquid formation followed by particle rearrangement played the principal role in densification.

Following new measurements of PVT properties, the values of the CO2 fugacity coefficients (ϑco2) were obtained within the range of 200/2–1000°C and 500/2–10.000 bar. Under pressures exceeding 4 kbar a significant dependence of ϑco2 on pressures (δϑco2/ δP)T δϑco 2 /δT) P $ 0 is observed. Coordinates (T,P,XCO2) of high-temperature reactions of carbonation were investigated experimentally in the presence of H2O + CO2 fluid (mole fraction of carbon dioxide: XCO2 = 0.01–0.4): 1. (a) diopside + forsterite + 2 calcite = 3 monticellite + 2CO2; 2. (b) forsterite + calcite = monticellite + periclase + CO2; 3. (c) diopside + calcite = akermanite + CO2; 4. (d)akermanite + calcite = merwinite + CO2; 5. (e) anorthite + wollastonite + calcite = grossularite + CO2. Comparison of these data with experimental and calculated curves in the presence of pure CO2 made it possible to estimate the values of the CO2 activity coefficients. In terms of composition Xco2 $ 0.4, carbon dioxide is characterized by marked positive deviations from ideality with τco2 increasing while Xco2 decreases. On the basis of all available experimental data a general T,Pco2 diagram of the high-temperature part of the system was derived in addition to some petrogenetic diagrams (under Xco2 = 0.3) of optimum conditions of high-temperature contact metamorphism in the Earth's crust.

The phase assemblages of monticellite (CaMgSiO 4 ) were investigated in the pressure range 80–300 kbar at about 1000°C in a diamond-anvil cell with laser heating. Incorporating earlier work, the following phase transformations are found: where the percentages give the decreases in zero-pressure volume for the new assemblage. If merwinite is a stable mantle mineral phase, even in very small quantities (∼1 mole percent), the results imply that olivine might decrease substantially in amount in the lower part of the Earth's upper mantle. This study also suggests that the observed seismic discontinuities in the mantle should not be entirely attributed to high-pressure polymorphism or decompositions of individual mineral species, and that some discontinuities may result from chemical reactions between the individual phases.

Subsolidus and vapor-saturated liquidus phase relations for a portion of the system CaO-MgO-SiO 2 -H 2 O, as inferred from experimental data for the composition regions CaMgSi 2 O 6 -Mg 2 SiO 4 -SiO 2 -H 2 O and CaMgSi 2 O 6 -Mg 2 SiO 4 -Ca 3 MgSi 2 O 8 (merwinite)-H 2 O, are presented in pressure-temperature projection. Sixteen invariant points and 39 univariant reactions are defined on the basis of the 1 atm and 10 kbar (vapor-saturated) liquidus diagrams. Lack of experimental control over many of the reactions makes the depicted relations schematic in part. An invariant point involving orthoenstatite, protoenstatite, pigeonite, and diopside (all solid solutions) occurs at low pressure (probably between 1 and 2 kbar). At pressures below this invariant point, orthoenstatite breaks down at high temperature to the assemblage diopside + protoenstatite; with increasing temperature, the latter assemblage reacts to form pigeonite. At pressures above the invariant point, pigeonite forms according to the reaction diopside + orthoenstatite = pigeonite, and the assemblage diopside + protoenstatite is not stable. At 1 atm, both pigeonite and protoenstatite occur as primary liquidus phases, but at pressures above 6–7 kbar orthoenstatite is the only Ca-poor pyroxene polymorph which appears on the vapor-saturated liquidus surface. At pressures above approximately 10.8 kbar, only diopside, forsterite, and merwinite occur as primary liquidus phases in the system CaMgSi 2 O 6 -Mg 2 SiO 4 -Ca 3 MgSi 2 O 8 -H 2 O, in the presence of an aqueous vapor phase. At pressures between 1 atm and 10.2 kbar, both akermanite and monticellite also occur as primary liquidus phases. Comparison of the 1 atm and 10 kbar vapor-saturated liquidus diagrams suggests that melilite basalt bears a low pressure, or shallow depth, relationship to monticellite-bearing ultrabasites.

A MgO-monticellite (CaMgSiO4) ceramic has been observed with high resolution transmission electron microscopy (HR-TEM) and scanning transmission electron microscopy (STEM). Two samples were quenched at different rates, yielding different microstructures. The quenched sample (1.5×104°C/s) exhibits complete wetting of the grain boundaries by the liquid phase. The rapidly cooled sample (120°C/s) has monticellite or forsterite crystals growing from the MgO grains into the liquid phase. The growing crystallites are magnesium rich relative to the liquid composition. They also appear to grow rapidly with a columnar microstructure.

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.

Hydrothermal investigation of the bulk compositions Ca 19 Mg 4 Al 10 Si 17 O 68 (OH) 8 and Ca 19 Mg 3 Al 10 Si 18 O 68 (OH) 10 (+ or -4SiO 2 + H 2 O) has been conducted by using conventional cold seal and internally heated pressure apparatus at 320 degrees to 900 degrees C and 1 to 2 kb P fluid . Magnesium idocrase was readily crystallized from oxide mixes at 600 degrees C. The synthetic material is extremely fine grained and is nearly isotropic with an average refractive index of 1.698. The stability fields of idocrase and idocrase + quartz were reversibly determined using the synthetic phases as starting materials with run durations of between 6 and 45 days. The hightemperature decomposition of Mg idocrase is experimentally determined to be a continuous reaction in which the coexistence of idocrase and melilite + monticellite occurs over the temperature range of approximately 722 degrees C to 825 degrees C + or - 12 degrees C at 1 kb and 722 degrees C to 862 degrees C + or - 12 degrees C at 2 kb P fluid . Cell dimensions of the idocrase grown at 600 degrees C and 1 kb P fluid are a = 15.559(4)Aa and c = 11.805(4)Aa, and those of the idocrase grown at 800 degrees C and 1 kb P fluid are a = 15.546(4)Aa and c = 11.802(4)Aa. This small but statistically significant difference in a may indicate a minor difference in composition of the high- and low-temperature idocrases according to the above reaction. Above this temperature range, idocrase becomes unstable according to the reaction: idocrase = wollastonite + melilite + monticellite + H 2 O.The thermal stability of idocrase is greatly shifted toward lower temperatures in the presence of quartz with the dehydration reaction defined by: idocrase + 4 quartz = 5 grossular + 3 diopside + wollastonite + 4 H 2 O. This reaction was experimentally determined to occur at 393 degrees C + or - 10 degrees C (1 kb P fluid ) and 405 degrees C + 5 degrees C (2 kb P fluid . Using the present and previous experimentally determined results and ehemographie relationships in the system CaAl 2 Si 2 O 8 -CaMgSi 2 O 6 -CaSiO 3 -SiO 2 -H 2 O-CO 2 , isobaric T-X (sub CO 2 ) diagrams were constructed which indicate that idoerase in the presence of quartz should be stable only at temperatures lower than 400 degrees C and at X (sub CO 2 ) less than 0.015 at 2 kb P fluid . The experimentally determined P-T conditions for the stabilities of idoerase and idoerase + quartz are consistent with those deduced from natural parageneses of idoerase in skarns and regionally metamorphosed rocks. It is suggested that the growth and stability of idoerase implies a fluid phase with exceedingly low X (sub CO 2 ) .

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.

The effects of a silicate boundary phase on the high-temperature stress-strain behavior of MgO materials have been studied using a model system MgO-CaMgSiO4 (monticellite, CMS). Specimens were fabricated by hot-pressing, or by hot-pressing and annealing, and contained up to 15% silicate phase. The boundary phase consisted primarily of CMS. The stress-strain behavior of these specimens in the range 1200° to 1400°C was strongly dependent on the degree of continuity of the grain boundary phase and on the temperature.

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 Hoch-Arpshofen model was applied to the SiO2-CaO-MgO-Al2O3 system. First the binary interaction coefficients, obtained from the six binary systems, were used to calculate the Gibbs energy of formation of the ternary compounds present in the four ternary systems; then the calculated activities of SiO2, CaO, and Al2O3 were compared with the measured activities. The calculated Gibbs energies of formation of anorthite, gehlenite, and cordierite agree with the measured energies; the measured enthalpies of formation of akermanite, diopside, merwinite, and monticellite must be multiplied by 0.568 ± 0.031 to obtain agreement. The Gibbs energy of formation of 3CaO-MgO-2Al2O3 was also calculated. The calculated activity data agree with some authors' measurements and not with others.

Within a swarm of late middle Eocene subsilicic-alkalic diatremes, one diatreme 270 by 370 m and an associated dike contain common xenoliths of granulite and rare xenoliths of spinel peridotite and garnet peridotite. Six garnet lherzolite xenoliths have been found and these show a range of textures. Four are granular, and two are intensely sheared. Phlogopite is absent from the intensely sheared xenoliths and is thought to be primary in part in the granular xenoliths. Estimated temperatures and depths of equilibration of xenolith pyroxenes range from 920°C, 106 km (32 kbar) to 1315°C, 148 km (47 kbar). The xenoliths show increasing amounts of deformation with greater inferred depths of origin. The temperature-depth points suggest a segment of an Eocene geotherm for Montana which is similar in slope to the steep portion of the pyroxene-determined Lesotho geotherm (B oyd and N ixon , this volume) and is considerably steeper than typical calculated shield and continental geotherms at present. The steep trend could be a result of plate-tectonic shearing and magma ascension within an Eocene low-velocity zone. Preservation of intensely sheared textures requires rapid transport of material from about 150 km depth during active deformation of relatively dry rock. The occurrence of monticellite peridotite in this kimberlite diatreme suggests that magmas which crystallized to monticellite peridotite at relatively shallow depth could be one of the primitive types of kimberlite magma.

Enthalpies of solution of synthetic enstatite (Mg2Si2O6), forsterite (Mg2SiO4), akermanite (Ca2MgSi2O7), monticellite (CaMgSiO4), and merwinite (Ca3MgSi2O8) and their component oxides were determined in eutectic (Li, Na)BO2 at 1073 K. Resulting enthalpies of formation at 1073 are enstatite: −8.10 ± 0.42 kcal ; forsterite: −14.23 ± 0.45 kcal ; akermanite: −42.60 ± 0.39 kcal ; monticellite: −25.05 ± 0.41 kcal ; and merwinite: −51.10 ± 0.49 kcal . The value for the synthetic monticellite of composition Mo.965Fo.035 was corrected slightly for non-stoichiometry based on experimental monticellite-forsterite phase equilibrium relations. The enthalpies of formation of enstatite and forsterite are somewhat less negative than yielded by several other solution calorimetric studies but are in good agreement with the recent Pb2B2O5 solution calorimetry of Kiseleva et al. (1979), and are in good agreement with values to be derived from reliable phase equilibrium data in the system MgO-Al2O3-SiO2. The enthalpies of formation of akermanite, monticellite and merwinite are all much less negative than values tabulated by robie et al. (1978) and helgeson et al. (1978) but are shown to be compatible with reliable phase equilibrium data for the system CaO-MgO-SiO2, whereas the tabulated values are not. Several methods of analysis yield an entropy of monticellite at 1000 K of 69.9 ± 0.2 cal/K .

The heat capacity of a natural monticellite (Ca 1.00 Mg .09 Fe .91 Mn .01 Si 0.99 O 3.99 ) measured between 9.6 and 343 K using intermittent-heating, adiabatic calorimetry yields C p 0 (298) and S 298 0 of 123.64 ± 0.18 and 109.44 ± 0.16 J · mol −1 K −1 respectively. Extrapolation of this entropy value to end-member monticellite results in an S 0 298 = 108.1 ± 0.2 J · mol −1 K −1 . High-temperature heat-capacity data were measured between 340–1000 K with a differential scanning calorimeter. The high-temperature data were combined with the 290–350 K adiabatic values, extrapolated to 1700 K, and integrated to yield the following entropy equation for end-member monticellite (298–1700 K): S T 0 ( J · mol −1 K −1 ) = S 298 0 + 164.79 In T + 15.337 · 10 −3 T + 22.791 · 10 5 T −2 − 968.94. Phase equilibria in the CaO-MgO-SiO 2 system were calculated from 973 to 1673 K and 0 to 12 kbar with these new data combined with existing data for akermanite ( Ak ), diopside ( Di ), forsterite ( Fo ), merwinite ( Me ) and wollastonite ( Wo ). The location of the calculated reactions involving the phases Mo and Fo is affected by their mutual solid solution. A best fit of the thermodynamically generated curves to all experiments is made when the S 0 298 of Me is 250.2 J · mol −1 K −1 less than the measured value of 253.2 J · mol −1 K −1 . A best fit to the reversals for the solid-solid and decarbonation reactions in the CaO-MgO-SiO 2 -CO 2 system was obtained with the ΔG 0 298 ( kJ · mole −1 ) for the phases Ak (−3667), Di (−3025), Fo (−2051), Me (−4317) and Mo (−2133). The two invariant points − Wo and − Fo for the solid-solid reactions are located at 1008 ± 5 K and 6.3 ± 0.1 kbar, and 1361 ± 10 K and 10.2 ± 0.2 kbar respectively. The location of the thermodynamically generated curves is in excellent agreement with most experimental data on decarbonation equilibria involving these phases.

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.

The effects of the presence of a silicate boundary phase on the high-temperature creep behavior of a model refractory system MgO--CaMgSiO/sub 4/ (monticellite, CMS) were studied at 1200 to 1450/sup 0/C. A change in the dominant mechanism of deformation was determined with increasing temperature and decreasing applied stress. It was concluded that, at 1200/sup 0/C, deformation is controlled by a dislocation mechanism in the MgO framework, whereas at higher temperatures creep is the result of simultaneous mechanisms but dominated by viscous deformation of the silicate boundary region.

SummaryCell dimensions obtained from X-ray powder photographs of twenty-four natural olivines and one synthetic forsterite have been related to the cation contents by a new statistical procedure developed by M. H. Hey. Unlike conventional statistical analysis, which assumes error only in one parameter, this procedure simultaneously considers the estimated errors in all variables.Linear terms in Ca, Mn, Mg (or Fe(≡ 1-Mg-Ca-Mn)) satisfactorily account for the cell dimensions, and there was no need to invoke a term in Mg2. Since there are three cell dimensions and three chemical unknowns, it is theoretically possible to estimate the major cations in olivine just from the cell dimensions. However, the coefficients for Mn and Fe are so similar and the ranges of Ca and Mn are so small that the technique would be impractical.Data for ideal (Mg,Fe) olivines were estimated by adjusting the cell dimensions by linear extrapolation from the cell dimensions of tephroite and monticellite. A simple chemical term was sufficient to account for each cell dimension. The linear relation between cell volume and Mg is consistent with the complete disorder of Mg and Fe revealed by parallel single-crystal X-ray studies.The cell dimensions of a synthetic fayalite deviate significantly from those of natural fayalites after correction for the effects of Ca and Mn substitution in the latter: some structural or chemical difference, probably involving ferric iron, is indicated.No superstructure lines have been found, in contradiction to Eliséev's data.

Possible reactions occurring in basic brick were first explored by studying (a) binary mixtures of sesquioxides or magnesia spinels and (b) three silicates, namely forsterite, monticellite, and di-calcium silicate. Compositions ranging from 10 to 90% of each constituent were pressed into cylinders and heated at 100°C intervals between 800°C and a maximum of 1700°C or until melting occurred. Bulk density and volume changes were recorded and X-ray diffraction was used to explore chemical reactions. Reactions between the three silicates and three chrome ores were also studied. Since the most refractory specimens were those containing magnesiochromite as the spinel constituent, the effect of free magnesia as a third component in these series was finally explored.

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.

SUMMARY. The effects of hydrothermal treatments on gel mixtures and synthetic minerals in the C3S2-M8S2 and C2S-M2S regions of the CaO-MgO-SiO~ system have been investigated. The products formed in the temperature range I80-35o ~ at pressures up to 2zo N/mm* were identified, x The reactants generally behaved as simple mixtures of binary silicates and their products agreed well with existing data for reactions in the CaO-SiO2-H20 and MgO-SiO2-I-I20 systems. An unidentified phase that resulted from the hydration of ~kermanite could be a new compound in the quaternary CaO-MgO-SiO~-H20 system. There was no evidence to indicate that a magnesium analogue of kilchoanite can be formed from materials that are isostructural with 7-Ca2SiO,. RESULTS of earlier studies in the Ca2SiO4-SiO2-H20 region of the CaO-SiO2-H20 system by Speakman and Taylor (1965, 1967) and Speakman (I968) showed that a material consisting largely of kilchoanite was formed when a mixture of 7-CasSiO4 and quartz, having an over-all CaO/SiO~ ratio of 1"5, was treated hydrothermally at 18o ~ The thermodynamic stability of kilchoanite formed at low temperatures and pressures has been the subject of much discussion (Speakman and Taylor, 1967; Roy and Harker, 196o; Roy and Johnson, 1965) and although the point has not been finally settled, current opinion favours the view that it is a non-equilibrium phase under these conditions. The explanation for the readiness with which 7-Ca2SiO4 can form kilchoanite is almost certainly connected with the structural and chemical similarities that exist between them. The equilibrium products xonotlite and hillebrandite, on the other hand, have very different crystal structures. The present work was undertaken to investigate the possible formation of a magnesium substituted kilchoanite from forsterite and monticellite, which are isostructural with 7-Ca2SiO~. The study was later extended to include an examination of the products formed from several other compositions on the join Ca~Si2OT-MgaSi2OT. Four compositions were thought to be sufficient to give all the information required to detect and characterize a magnesium analogue of kilchoanite and any other new phases formed in this particular region. More emphasis was placed on the nature of the starting materials and on their influence on the type of products formed than on the number of compositions examined, since the formation of kilchoanite is believed to be a structure-dependent phenomenon and the starting material all important.

The constitution and mineralogy of Indian open hearth and L. D. slags were investigated. Chemical, petrographic and X-ray diffraction methods were followed. All the slags were high in CaO. β-dicalcium silicate, wustite and nagelschmidtite were the predominant mineral phases present. Other phases identified were dicalcium ferrite, tricalcium silicate, monticellite, and brownmillerite. Metallic iron occurred in varying proportions in all the slags. Free lime was present only in L. D. slags.