Vitreous forsterite (Mg<sub>2</sub>SiO<sub>4</sub>): Synthesis, structure, and thermochemistry

Tangeman, Jean A.; Phillips, Brian L.; Navrotsky, Alexandra; Weber, Jacques; Hixson, April D.; Key, Thomas S.

doi:10.1029/2000gl012222

Cited by 105 publications

(93 citation statements)

References 24 publications

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“…The glass starting materials were synthesized from oxide starting mixtures by the containerless method under reducing conditions to prevent iron oxidation (36). The starting materials were powdered and mixed with 10 wt% gold, used as a pressure calibrant and laser absorber.…”

Section: Methodsmentioning

confidence: 99%

Mineralogical effects on the detectability of the postperovskite boundary

Grocholski

Catalli

Shim

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

106

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The discovery of a phase transition in Mg-silicate perovskite (Pv) to postperovskite (pPv) at lowermost mantle pressure-temperature (P − T ) conditions may provide an explanation for the discontinuous increase in shear wave velocity found in some regions at a depth range of 200 to 400 km above the core-mantle boundary, hereafter the D 00 discontinuity. However, recent studies on binary and ternary systems showed that reasonable contents of Fe 2þ and Al for pyrolite increase the thickness (width of the mixed phase region) of the Pv − pPv boundary (400-600 km) to much larger than the D 00 discontinuity (≤70 km). These results challenge the assignment of the D 00 discontinuity to the Pv − pPv boundary in pyrolite (homogenized mantle composition). Furthermore, the mineralogy and composition of rocks that can host a detectable Pv → pPv boundary are still unknown. Here we report in situ measurements of the depths and thicknesses of the Pv → pPv transition in multiphase systems (San Carlos olivine, pyrolitic, and midocean ridge basaltic compositions) at the P − T conditions of the lowermost mantle, searching for candidate rocks with a sharp Pv − pPv discontinuity. Whereas the pyrolitic mantle may not have a seismologically detectable Pv → pPv transition due to the effect of Al, harzburgitic compositions have detectable transitions due to low Al content. In contrast, Al-rich basaltic compositions may have a detectable Pv − pPv boundary due to their distinct mineralogy. Therefore, the observation of the D 00 discontinuity may be related to the Pv → pPv transition in the differentiated oceanic lithosphere materials transported to the lowermost mantle by subducting slabs.T he lower mantle is a multicomponent (MgO, SiO 2 , FeO, Al 2 O 3 , CaO, Na 2 O, etc.), multiphase (magnesium silicate perovskite (Pv), ferropericlase (Fp), calcium silicate perovskite (Ca-Pv), silica, calcium-ferrite-type aluminous (CF) phase, etc.) system and understanding the effects of chemistry and mineralogy on the depths and thicknesses of mantle phase boundaries is of fundamental interest. Although the discovery of the Pv → pPv transition at lowermost mantle P − T conditions (1-3) has been invoked as an explanation for the D 00 discontinuity, the combined effect of mineralogy and chemistry remain unresolved. Some recent studies (4-14) demonstrated large effects of chemical composition on the depth and thickness of the Pv → pPv boundary. The depth range over which the Pv → pPv transition occurs in mantle-related systems is much wider (4, 5) than the seismically constrained thickness (15,16). It also occurs close to the coremantle boundary (CMB) (135 GPa) even at 2,500 K with a positive Clapeyron slope, making it possible that the transition may not occur at all in the hotter lowermost mantle. Although the effect of Fp on the Pv → pPv transition has been modeled (4), other mineralogical effects are not fully understood due in part to our poor understanding of Al partitioning in these systems. Direct measurements on different mantle-related compositio...

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Section: Methodsmentioning

confidence: 99%

Mineralogical effects on the detectability of the postperovskite boundary

Grocholski

Catalli

Shim

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

106

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“…Glasses produced in the MgO-SiO 2 system between the compositions of the two important mantle minerals forsterite and enstatite show changes in structure [17,18] that coincides with changes in the relaxation properties of these glasses [19,20]. These rheological changes reflect differences in the configurational entropy of the liquid and in the terminology of Angell this is a change in the liquid fragility [7,21,22].…”

Section: Introductionmentioning

confidence: 99%

“…These rheological changes reflect differences in the configurational entropy of the liquid and in the terminology of Angell this is a change in the liquid fragility [7,21,22]. Glasses corresponding to the composition of forsterite (Mg 2 SiO 4 ), the most silica-poor glass studied in this system, is the most fragile, in other words it has a viscosity-temperature relation that departs from the Arrhenius law [19,20]. The more silica-rich glasses, with 38-50 mole% SiO 2 are stronger.…”

Section: Introductionmentioning

confidence: 99%

In situ diffraction studies of magnesium silicate liquids

2008

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Primitive MgO-SiO 2 liquids dominate the early history of the Earth and Terrestrial planets. The structures of these liquids and structure-dependent properties, such as viscosity and diffusion, are considered important in the evolution of these planets, however, MgO-SiO 2 liquids are refractory and do not form glasses easily and it is difficult to measure the structure of these liquids. Container-less synthesis techniques have been used to produce glasses that range in composition from 50 to 33% SiO 2 , corresponding to the compositions of two important mantle minerals: enstatite and forsterite. The structure of these glasses has been determined using combined neutron and high-energy diffraction and show changes in the short-range order as a function of composition. These changes include a jump in Mg-O coordination number at the limit to the formation of the silicate network in forsterite composition glass. These results imply a similar change in the structure of the liquid. Accordingly, the structures of forsterite and enstatite liquids have been determined using high-energy X-rays and a specialized sample environment, a containerless levitator. The main qualitative structural differences between MgSiO 3 and Mg 2 SiO 4 glasses are also observed in the melt. Liquid MgSiO 3 is interpreted as forming a relatively 'strong' network of SiO 4 tetrahedra, whereas the Mg 2 SiO 4 liquid is ''fragile'' and dominated MgO n (n = 4, 5, 6) polyhedra and highly mobile oxygen ions. The results differ significantly from previously reported X-ray diffraction data for liquid MgSiO 3 .

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“…Tangeman and coworkers succeeded in synthesizing MgO-SiO 2 glasses over a wide compositional range (7), covering the enstatite composition (MgSiO 3 ) to the forsterite composition (Mg 2 SiO 4 ), which can be considered as analogues of quenched melts from the Earth and Lunar mantle (8)(9)(10). The Mg 2 SiO 4 composition glass has been formerly synthesized using a rapid quench method and studied using vibrational spectroscopy (11,12), however, the advantage of the levitation technique is that it allows us to synthesize a high-purity bulk sample.…”

mentioning

confidence: 99%

“…The Mg 2 SiO 4 composition glass has been formerly synthesized using a rapid quench method and studied using vibrational spectroscopy (11,12), however, the advantage of the levitation technique is that it allows us to synthesize a high-purity bulk sample. The structure of these glasses was recently studied using theoretical simulation (13), spectroscopic measurements (7,(13)(14)(15), diffraction measurements (16)(17)(18)(19), and atomistic modeling on the basis of diffraction data (17)(18)(19) In this paper we model and analyze the structure of silica glass (SiO 2 ), enstatite glass (MgSiO 3 ), and forsterite (Mg 2 SiO 4 ) glass employing the RMC modeling technique and the density function theory (DFT) of electronic structure using measured and published synchrotron X-ray and neutron diffraction data (16)(17)(18). Special attention is paid to ring statistics, cavity volumes, and the connectivity of short-range structural units in the glasses.…”

mentioning

confidence: 99%

Relationship between topological order and glass forming ability in densely packed enstatite and forsterite composition glasses

Kohara

Akola

Morita

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

114

107

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The atomic structures of magnesium silicate melts are key to understanding processes related to the evolution of the Earth's mantle and represent precursors to the formation of most igneous rocks. Magnesium silicate compositions also represent a major component of many glass ceramics, and depending on their composition can span the entire fragility range of glass formation. The silica rich enstatite (MgSiO 3 ) composition is a good glass former, whereas the forsterite (Mg 2 SiO 4 ) composition is at the limit of glass formation. Here, the structure of MgSiO 3 and Mg 2 SiO 4 composition glasses obtained from levitated liquids have been modeled using Reverse Monte Carlo fits to diffraction data and by density functional theory. A ring statistics analysis suggests that the lower glass forming ability of the Mg 2 SiO 4 glass is associated with a topologically ordered and very narrow ring distribution. The MgO x polyhedra have a variety of irregular shapes in MgSiO 3 and Mg 2 SiO 4 glasses and a cavity analysis demonstrates that both glasses have almost no free volume due to a large contribution from edge sharing of MgO x -MgO x polyhedra. It is found that while the atomic volume of Mg cations in the glasses increases compared to that of the crystalline phases, the number of Mg-O contacts is reduced, although the effective chemical interaction of Mg 2þ remains similar. This unusual structure-property relation of Mg 2 SiO 4 glass demonstrates that by using containerless processing it may be possible to synthesize new families of dense glasses and glass ceramics with zero porosity.Earth science | glass structure G lasses can be synthesized by making use of a network former, such as B 2 O 3 , As 2 O 3 , SiO 2 , GeO 2 , or P 2 O 5 which form continuous three-dimensional networks, according to Zachariasen's theory (1). On the basis of this theory many ideas on glass formation have been proposed. One such idea by Cooper and Gupta proposed that a topologically disordered network is the key to understanding the origin of glass formation (2, 3). Indeed, it is well known that the silica glass network exhibits a broad ring distribution which is topologically disordered, and is made up of a connection of SiO 4 tetrahedra sharing oxygen atoms at the corners (4, 5). In contrast the corresponding crystalline phase has only 6-fold rings.Recently the use of the aerodynamic levitation technique combined with a laser heating system has expanded the glass forming range of many oxides, due to the avoidance of contact between the container walls and high-temperature melt (6). Tangeman and coworkers succeeded in synthesizing MgO-SiO 2 glasses over a wide compositional range (7), covering the enstatite composition (MgSiO 3 ) to the forsterite composition (Mg 2 SiO 4 ), which can be considered as analogues of quenched melts from the Earth and Lunar mantle (8-10). The Mg 2 SiO 4 composition glass has been formerly synthesized using a rapid quench method and studied using vibrational spectroscopy (11, 12), however, the advantage of the levitat...

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Vitreous forsterite (Mg₂SiO₄): Synthesis, structure, and thermochemistry

Cited by 105 publications

References 24 publications

Mineralogical effects on the detectability of the postperovskite boundary

Mineralogical effects on the detectability of the postperovskite boundary

In situ diffraction studies of magnesium silicate liquids

Relationship between topological order and glass forming ability in densely packed enstatite and forsterite composition glasses

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Vitreous forsterite (Mg2SiO4): Synthesis, structure, and thermochemistry

Cited by 105 publications

References 24 publications

Mineralogical effects on the detectability of the postperovskite boundary

Mineralogical effects on the detectability of the postperovskite boundary

In situ diffraction studies of magnesium silicate liquids

Relationship between topological order and glass forming ability in densely packed enstatite and forsterite composition glasses

Contact Info

Product

Resources

About

Vitreous forsterite (Mg₂SiO₄): Synthesis, structure, and thermochemistry