0086-21-58386256
Seifertite and stishovite, the two high-pressure polymorphs of silica, are discovered in the lunar regolith returned by Chang'E-5 mission. This is the very first confirmed existence of seifertite in returned lunar samples, which is the evidence that Chang'E-5 regolith contains impact ejecta from distant craters as suggested by the …
Stishovite, the highest pressure polymorph of silicon dioxide, may be an important mineral in some regions of the Earth's mantle. Fourier transform infrared spectroscopy has been used to determine the hydrogen content of …
Stishovite has a structure very different from the other silica polymorphs, inasmuch as it is based on the polymerization of octahedra, a structure identical to that of rutile (titanium dioxide), a mineral of low toxicity (Baur and Khan 1971). Both stishovite and coesite exhibit minimal toxicity in vitro and in vivo (Table 1). Two additional ...
Orientation groups 2/3 and 6/7 define a mirror plane passing through [001]. (c) Stishovite has point-group symmetry 4/m 2/m 2/m; inserting the additional mirrors implied by this symmetry shows that one of them goes through groups 2 and 3, two others go through groups 6 and 7, respectively, and the last passes between groups 4 and 5, …
In-situ synchrotron X-ray diffraction experiments were conducted using the SPEED-1500 multi-anvil press of SPring-8 on stishovite SiO2 and pressure-volume-temperature data were collected at up to 22.5 GPa and 1,073 K, which corresponds to the pressure conditions of the base of the mantle transition zone. The analysis of room …
Hydrothermal experiments aiming at the crystal growth of stishovite near ambient pressure and temperature were performed in conventional autoclave systems using 1 M (molar) NaOH, 0.8 M Na2CO3, and pure water as a mineralizing agent. It was found that the hydrothermal metastability of stishovite and coesite is very different from the thermal …
Transformation of stishovite to a denser phase at lower-mantle pressures Kathleen J. Kingma, Ronald E. Cohen, Russell J. Hemley a Ho-kwang Mao Geophysical Laboratory and Center for High-Pressure ...
Stishovite is also detected in the matrix, where it has a less euhedral shape (Fig. 7). We surmise that it crystallized late in the matrix and that growth initiated from the remaining silicate melt (with growth …
Post-stishovite phase transition boundary influenced by Al content in stishovite. (a) The post-stishovite transition pressure as a function of the Al content in mol% at 300 K. The dashed line is the best polynomial fit to our data using 55 GPa as the transition pressure of the pure SiO 2 by Zhang et al. .
Stishovite (SiO 2 with the rutile structure and octahedrally coordinated silicon) is an important high-pressure mineral. It has previously been considered to be …
Stishovite: Ross N L, Shu J F, Hazen R M, Gasparik T (1990) High-pressure crystal chemistry of stishovite American Mineralogist 75 739-747: 1990: 0: 293: 0001307: Stishovite: Ross N L, Shu J F, Hazen R M, Gasparik T (1990) High-pressure crystal chemistry of stishovite American Mineralogist 75 739-747:
For the first time in the sixty years since the synthesis of stishovite, we report unambiguous evidence of stishovite formed in the deep Earth. A minimum pressure of about 7.5 GPa at 1000 °C is necessary for the formation of stishovite, corresponding to a depth of about 230 km. In this manuscript we report the identification of stishovite …
Introduction. Stishovite, a high-pressure polymorph of SiO 2 with a rutile structure, is the hardest oxidic material with a hardness of about 33 GPa and has been the subject of intense studies. 1−14 Despite this extraordinary property and its thermal metastability up to ca. 500 °C at ambient pressure, it has not found applications as an …
Stishovite in Béréba is formed through a solid–solid phase transition from original quartz/cristobalite. TEM observations with electron-beam irradiation indicate that stishovite vitrified immediately, implying that stishovite is very sensitive to heating. Some stishovite might become amorphous during adiabatic decompression.
Stishovite is known to undergo a ferro-elastic phase transition to the orthorhombic CaCl 2-type structure above 50 GPa (Fischer et al., 2018; Tsuchida & Yagi, 1989). It has been suggested that this …
The Mineral stishovite. Stishovite is an extremely rare mineral forming only from the impact of a meteorite through the metamorphism of Quartz at extremely high temperatures. It is …
The nitrogen solubility in stishovite varied from 90 ppm (μg/g) to 404 ppm (μg/g). Stishovite can incorporate higher concentrations of nitrogen than bridgmanite …
Recently, Nishiyama et al. synthesized a nanostructural form of stishovite named nano-polycrystalline stishovite (NPS), which exhibits remarkably high fracture toughness of about 10 MPa·m 1/2, according to Vickers indentation fracture measurements, while retaining high hardness (7, 8).Because NPS is made by simply applying high …
A Rietveld structural analysis of stishovite, with angle-dispersive x-ray diffraction synchrotron source at the European Synchrotron Radiation Facility, confirmed a CaCl 2 form of stishovite distortion at 54 ± 1 gigapascals but confirmed no further phase transformation up to 120 gigapascals. The deviatoric stress that is usually encountered …
1 Introduction. Stishovite is a high-pressure polymorph of silica (SiO 2) and is stable above 9 GPa at 1,000°C, with a tetragonal structure (space group P4 2 /mnm). …
The SiO 2 polymorph stishovite forms at high pressure (), and has been found in highly shocked rocks ().The existence and stability of post-stishovite silica (SiO 2 polymorphs denser than stishovite) have been …
Stishovite was formed by heating a-quartz or amorphous silica at pressures of up to 92 G Pa; on heating at 108 and 124 G Pa, however, the materials crystallized into a CaClrtype structure,
STISHOVITE is the highest pressure polymorph of silica. It possesses the rutile structure with a density of 4.28 g cm-3 and is characterised by sixfold coordination of silicon by oxygen. Previous ...
The working principle of primary crushers varies depending on the type of crusher, but generally, they work by reducing the size of the material through compression or impact. In jaw crushers, the material is fed into the crushing chamber and is crushed between a fixed jaw and a movable jaw. Gyratory crushers work by crushing materials …
[1] In situ P-V-T measurements of stishovite have been performed throughout its stability field from 17 to 54 GPa and from 300 to 1700 K, by using a sintered-diamond multianvil apparatus and synchrotron radiations. The P-V-T equation of state of stishovite was precisely determined on the basis of the Mie-Grüneisen-Debye model …
The metastable melting curve of stishovite is a smooth interpolation between a triple point (coesite, stishovite, liquid) and P-T conditions at 3 GPa and room temperature (ΔG between stishovite ...
Stishovite, high-pressure, metastable polymorph of silica (SiO2), having a rutile-type tetragonal structure; silicon is in six-fold coordination with oxygen while each oxygen atom is shared with three silicon atoms. Stishovite was first discovered in sandstone that had been converted to glass at
Stishovite (Stv) is a high-pressure polymorph of silica (SiO 2) and could occupy ~23% by volume in the subducted oceanic crust (10, 11).It is known as a NAM but recent experiments (12–14) revealed intriguing water incorporation phenomena in high-pressure synthesized Stv.The water solubility of pressure-quenched Al-free Stv crystals …
Lakshtanov et al. (2007) showed that incorporation of aluminum and some water into SiO 2 significantly reduces the post-stishovite transition pressure in SiO 2.This discovery suggested that the ferroelastic post-stishovite transition in subducted MORB crust could be the source of reflectors/scatterers with low shear velocities observed in …
Stishovite is known as a major component of subducted oceanic basalt, and recent experiments have reported that it can incorporate significant amounts of water in its crystal structure. Here, we show that, at the pressure–temperature conditions of a mantle geotherm, stishovite may be a key phase for transporting water into the deep mantle ...