Showing papers on "Tridymite published in 1982"
TL;DR: In this paper, it was determined that the high modal abundances of merrillite and tridymite in most mesosiderites are attributable to redox reactions between silicates and P-bearing Fe-Ni metal within a limited T-fO2 range at low pressure.
35 citations
TL;DR: The principal components of secondary mineral assemblages found in Pasco Basin basalts are iron-rich smectite (nontronite), clinoptilolite, and silica as mentioned in this paper.
Abstract: The principal components of secondary mineral assemblages found in Pasco Basin basalts are iron-rich smectite (nontronite), clinoptilolite, and silica. Silica occurs as quartz, cristobalite, tridymite, and opal-CT. Extractable iron within the nontronite suggests the presence of an iron-bearing oxyhydroxide phase intercalated with the nontronite. Other components present in minor or trace amounts are mordenite, celadonite, apatite, pyrite, phillipsite, gypsum, erionite, and chabazite. The generalized precipitation sequence with time and/or depth was found to be clay (usually nontronite) clinoptilolite silica and/ or clay. Nontronite, the first phase to form, is present at nearly al sampled depths. Clinoptilolite is apparently restricted to depths below about 350 m. Quartz is ubiquitous whereas opal and cristobalite appear to be abundant only below 600 m. Mordenite occurs only at depths below about 900 m, which correlates roughly with the first occurrence of dissolution-etched clinoptilolite. These observations as well as comparisons with data on secondary mineral assemblages from other basaltic and felsic systems suggest that the geochemical evolution of Pasco Basin basalts probably occurred under conditions similar to those existing today.
29 citations
TL;DR: In this article, the authors compared the analytical results of the 4πr3(ϱ(r)−ϱ0) function with the experimental RDF for silica glass.
Abstract: Radial distribution functions (RDF's) calculated from the bonding topologies of quartz, cristobalite, tridymite and a 1412 atom model of silica glass (35 A in diameter) have been compared with the experimental RDF for silica glass. The functions, 4πr3(ϱ(r)−ϱ0), computed over the range 0 < r < 20 A from the known structures of quartz, cristobalite, tridymite and the 1412 atom model have been compared with the corresponding function for silica glass by means of correlation functions, giving 0.26, 0.69, 0.82 and 0.91, respectively (0.00 would indicate no correlation, and 1.00, perfect positive correlation). Cristobalite and tridymite are composed entirely of six-membered rings of silicate tetrahedra, whereas the model contains both six- and five-membered rings in a ratio of 2.6:1. The correlation coefficients suggest that the six-membered rings of the type present in tridymite play a dominant role in silica glass, but that other ring sizes are important and result in the higher correlation coefficient for the 1412 atom model. While the correspondence in RDF's is encouraging, the model RDF does not fit the experimental curve to within the accuracy of the experiment. Perhaps the model is not large enough to represent adequately, in a statistical fashion, all the configurations present in a macroscopic sample.
27 citations
TL;DR: The high-form is hexagonal, probably P63mc, with a=5.30(1), c=8.65(1)A as mentioned in this paper, and the Zellengleichen subgroup relations are found among these three polymorphs.
Abstract: Kalsilite shows the domain structure corresponding to the disordered oxygen atoms at two mirror equivalent sites. The domain structure was considered to be due to the high-low inversion, and the structural model of the high-form was constructed. The heating experiment was carried out, which revealed that the X-ray powder pattern changes at 1138 K. It was confirmed that kalsilite undergoes a displacive transformation like quartz and tridymite. The high-form is hexagonal, probably P63mc, with a=5.30(1), c=8.65(1)A. The high-form was also considered to be divided into two groups, high-kalsilite (P63mc) and disordered high-kalsilite (P63⁄mmc). The Zellengleichen subgroup relations are found among these three polymorphs.
14 citations
Patent•
11 Nov 1982
TL;DR: In this article, the authors proposed to prevent the peeling of enameled ceramic from the base metal by adding cristobalite and/or tridymite to a ceramic having a specific thermal expansion coefficient.
Abstract: PURPOSE:To prevent the peeling of enameled ceramic from the base metal, by adding cristobalite and/or tridymite to a ceramic having a specific thermal expansion coefficient, thereby bringing the thermal expansion coefficient of the ceramic closer to that of the metal base. CONSTITUTION:In the preparation of ceramic for enameling the base metal of a dental crown or an ornament, the peeling of the ceramic from the metal after enameling the metal with the ceramic can be prevented bybringing the thermal expansion coefficient of the ceramic closer to that of the metal. This can be achieved by adding 1-60% cristobalite and/or tridymite to a ceramic containing e.g. 70-75% SiO2, 0.3-3.1% Al2O3, 4.6-9.6% CaO, 0.3-4.3% MgO, and 15- 17% Na2O and /or K2O and having a thermal expansion coefficient of >=85X 10 , crushing the mixture, kneading with water, shaping in the form of a rod, etc., bakig at 800 deg.C, and using the product as a raw material of the objective ceramic.
7 citations
TL;DR: In this paper, a method was developed for determining the amount of phases in specimens containing crystalline constituents of silica, based on measuring the relationship between the x-ray diffraction lines and the concentration of the phases using an independent, external standard.
Abstract: A method was developed for determining the amount of phases in specimens containing crystalline constituents of silica. The method is based on measuring the relationship between the x-ray diffraction lines and the concentration of the phases using an independent, external standard. The average error in the measurement of the amount of crystalline phases is ∼2–3% with a sensitivity of ∿0.5% for quartz and 1–2% for cristobalite and tridymite. Measuring the concentration of each phase with two independent lines tends to increase the accuracy of the analysis, which enables us to control the determination and increase its accuracy.