Topic
Tridymite
About: Tridymite is a research topic. Over the lifetime, 840 publications have been published within this topic receiving 14831 citations.
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TL;DR: In this paper, the existence of stable, super-liquidus immiscibility between silica- and Fe-rich multicomponent melts at temperatures above 1100 °C was tested in a 1-atm gas-mixing furnace.
Abstract: Here we report the results of an experimental study aimed at testing the existence of stable, super-liquidus immiscibility between silica- and Fe-rich multicomponent melts at temperatures above 1100 °C. Four pairs of the potentially immiscible compositions were tested in a 1-atm gas-mixing furnace (Ar/H2-CO2 gas mixture) at 1150 and 1200 °C and at the oxygen fugacity corresponding to that of the QFM buffer. Pre-synthesized pairs of the silica-rich and Fe-rich starting compositions were loaded in Pt wire loops, fused separately at 1300 °C, then brought in contact and kept at constant experimental temperature for more than 24 h. Three pairs of compositions out of four used in this study did not mix. Some temperature-dependent chemical re-equilibration was observed in the Fe-rich liquid phase but, in the cases of immiscibility, the two liquids remained compositionally distinct and showed sharp compositional gradients at contacts. One pair of liquids crystallized some tridymite, whereas the other compositions were clearly above the liquidus. Overall, the results of the experiments are in good agreement with the earlier centrifuge study and confirm the existence of stable, super-liquidus immiscibility in some Fe-rich basaltic-andesitic compositions at temperatures up to 1200 °C.
18 citations
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TL;DR: In this article, a ternary phase equilibrium diagram is presented for the system Mg0-Mn0-Si02 at liquid compositions of (a) 32 MgO, 5 MnO, 63 SiO2 and (b) 36 Mg O, 5.5 Mn O, 58.5 SO,. Each of these liquids is in equilibrium with a hodonite (Mn-SiO) and a high enstatite (MgSiO,) solid solution.
Abstract: A ternary phase equilibrium diagram is presented for the system Mg0-Mn0-Si02. Two peritectic points exist at 1536° and 1538°C. at liquid compositions of (a) 32 MgO, 5 MnO, 63 SiO2 and (b) 36 MgO, 5.5 MnO, 58.5 SO,. Each of these liquids is in equilibrium with a hodonite (Mn-SiO,) and a high enstatite (MgSiO,) solid solution, the third crystalline phase being cristobalite (SiO2) with (a) and olivine ((Mg,Mn]2,Si04) with (b). Metasilicate solid solutions form a congruently melting rhodonite series in the central part of the MgSi03-MnSi03 join, but melt incongruently to olivine plus liquid at the MgSiO3 end and to tridymite plus liquid at the MnSi03 end. X-ray diffraction data are given for two new high enstatite solid solution structures. Rhodonite solid solutions form a continuous structural series extending from MnSi0, to 94.5 weight % MgSi03. Continuous series of solid solutions exist between Mg,Si04 and Mn2SiO4 and between MgO and MnO. Compositional data are given for coexisting condensed phases, and courses of crystallization are described for certain ternary mixtures. A plot is presented of variation of refractive index of glasses which form an almost colorless series in the region of the rhodonite and high enstatite fields. The quenching technique was used in the investigation, with oxygen partial pressure controlled to maintain manganese as Mn2+.
18 citations
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TL;DR: In this article, the potentially reactive components of Beltane opal rock are identified as opal-A, opalC and tridymite, and the rate of dissolution of each component in 3 molar sodium hydroxide solution is followed using X-ray powder diffraction.
18 citations
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TL;DR: The framework structure of a new sodium zinc arsenate, produced by dehydration of the Na 6 (ZnAsO 4 ) 6 ·8 H 2 0 sodalite analog, has been solved by a simulated annealing method as mentioned in this paper.
18 citations
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TL;DR: In this paper, the mechanisms and rates of the reactions are discussed, and the problem of determining the chemically combined water in amosite and other minerals of similar composition is considered, and a broad exotherm on the d.t.a.
Abstract: Summary. When amosite (fibrous grunerite, F%.sMgl.sSisO~(OH)~), is heated in argon or nitrogen, physically combined water is lost up to 500-700 ~ C. Above 500~ (static) or 700~ (dynamic), dehydroxylation occurs endothermieally, giving a pyroxene as the main product. Under dynamic heating conditions, part of the hydroxyl water is lost as hydrogen, with concurrent oxidation of the iron. At about 1000 ~ C the pyroxene is decomposed to olivine and cristobalite ; at about 1100 ~ C melting begins. In oxygen or air, physically combined water is again lost below 500-700 ~ C. At 350-1200 ~ C a sequence of overlapping dehydrogenation, oxygen absorption, and dehydroxylation reactions occurs, which gives rise to a broad exotherm on the d.t.a, curve. The main products (for static heating conditions) are an oxyamphibole at 350-800 ~ C, and a spinel, hematite, a pyroxene, and X-ray amorphous material at 800-1100 ~ C. Silica crystallizes as cristobalite at 1100-1350 ~ C, and as tridymite at 1450 ~ C. Most of the products in either neutral or oxidizing atmospheres are formed topotactically. The mechanisms and rates of the reactions are discussed, and the problem of determining the chemically combined water in amosite and other minerals of similar composition is considered.
18 citations