Tridymite

About: Tridymite is a research topic. Over the lifetime, 840 publications have been published within this topic receiving 14831 citations.

Liquid–Solid Equilibria in the System FeO–NiO–Fe2O3–SiO2

Abstract: Liquidus and solidus phase relations have been determined for the system NiO-iron oxide–SiO2 in air and in CO2. In both cases the system is simple in that it contains only three primary crystalline phases: spinel (Fe3O4–NiFe2O3 solid solution), oxide (“FeO”–NiO solid solution) and SiO2, either tridymite or cristobalite. There is only one liquidus invariant point at which the above crystalline phases coexist with liquid (and the gas phase). In air, the invariant point (a eutectic) is at 1524°C, and a temperature maximum is present along the spinel–silica liquidus boundary curve at 1540°C. In CO2, the silica + spinel + oxide + liquid invariant temperature is considerably lower: 1433°C. Combination of these data with those obtained previously for the same system under strongly reducing conditions (CO2–CO gas mixtures of ratios only slightly above those of equilibrium coexistence of the oxide phases with Fe–Ni alloy) makes it possible to draw the main features of phase relations in the quaternary system FeO–NiO–Fe2O3–SiO2. This system also is relatively simple, in that only five crystalline phases are present in equilibrium with liquids, viz, silica (cristobalite or tridymite), olivine (Fe2SiO4-Ni2SiO4 solid solution), spinel (Fe3O4-NiFe2O4 solid solution), hematite (Fe2O3), and oxide (“FeO”–NiO solid solution). There is only one quaternary liquidus invariant point in the system, characterized by the equilibrium coexistence of silica, olivine, spinel, oxide, and liquid, at a temperature of ∼ 1410°C and an oxygen pressure of the gas phase of ∼10−5 atm.

Nano-structure of the Cristobalite and Tridymite Stacking Sequences in the Common Purple Opal from the Gevrekseydi Deposit, Seyitomer-Kutahya, Turkey

Abstract: The strata that include the fine purple opal formations examined in this paper from the magmagenetic hydrothermal dissolutions. The opals are locally known as Gevrekseydi purple opals. These opal-bearing strata are deposited in volcanic lavas and tuffs in the SeyitomerKutahya region of western Turkey. The purple opals are common-type and attractive gem-quality, and they are sold on the worldwide gem markets. We conducted mineralogical investigations to clarify their silica building components, measure their nano-size, and determine their origins. The opals are an opal-CT (opal-cristobalite/tridymite)- type silica polymorph with the variable number of cristobalite and tridymite layers. The cristobalite and tridymite stacking sequences were evaluated in terms of maturation, crystallite size, and genesis of the opaline silica material. These sequences are modelled using X-ray diffraction patterns. The relationship between the crystallite size and full width at half maximum values of the Gevrekseydi purple opals were also examined using X-ray diffraction patterns. The crystallite sizes were found to be L=17 nm for the main opal-CT peak (4.09 A), L=23 nm for the shoulder opal-CT peak (4.29 A), and L=27 nm for the opal-CT/C peak (2.51 A).Given the relationship between the crystallite size and maturation of opal-CT, the Gevrekseydi volcanic common purple opals are most likely in a stage of early to mid maturation

On the surface potential of pneumoconiotic dusts.

Abstract: Summary The mobility of silicogenic dust samples (cristobalite, erosil, tridymite, silicon dioxide and vitrinite) was studied by microelectrophoresis, which showed that they differed in surface potential. A relationship was found between surface potential and severity of tissue damage.

Tridymite pseudomorphs after wood in virginian lower cretaceous sediments.

Abstract: Fossil wood composed of tridymite is abundant in Patuxent (Lower Cretaceous) arkose on Hazel Run, Fredericksburg, Virginia. X-ray diffraction studies of the tridymite indicate that it has a disordered structure in which hexagonal close packing predominates. The specimens, which contain trace amounts of aluminum, iron, and other elements, are soft and fibrous, varying from white to shades of brown.

Influence of MgO on the phase equilibria in the CuOx-FeOy-MgO-SiO2 system in equilibrium with copper alloy - part I: methodology and liquidus in the tridymite primary phase field

Abstract: Phase equilibria in the ‘Cu2O’–‘Fe2O3’–MgO–SiO2 system in equilibrium with copper alloy have been investigated at temperatures between 1 100 and 1 250 °C. A high-temperature equilibration/quenching/electron probe micro-analysis technique has been used to accurately determine the liquid and solid compositions. The standard methodology has been modified to accurately determine the phase equilibria and liquidus in this particular chemical system. Results on phase equilibria in the tridymite primary phase field, including the tridymite–pyroxene, tridymite–spinel and tridymite–pyroxene–spinel phase boundaries, are reported. The study demonstrates the validity of the method and provides new data on the effect of MgO on the tridymite liquidus temperatures. Increasing MgO concentration was found to decrease the tridymite liquidus.