A new aluminocalcic high-pressure phase as a possible host of calcium and aluminium in the lower mantle

Madon, M.; Castex, Joëlle; Peyronneau, J.

doi:10.1038/342422a0

Cited by 44 publications

(14 citation statements)

References 20 publications

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“…It has been shown that KAlSi308 and NaA1Si,08 transform at 1300 K into a denser phase with the hollandite structure at 12 GPa and 21 to 24 GPa, respectively (3, 4). Several other silicates with the hollandite structure have also been synthesized (5)(6)(7). Experiments performed in the KA1Si308-NaA1Si308 system at pressures between 5 and 23 GPa and at temperatures ranging from 1000 to 1500 K have provided more complex results (8).…”

mentioning

confidence: 99%

Natural NaAlSi ₃ O ₈ -Hollandite in the Shocked Sixiangkou Meteorite

Gillet

Chen

Dubrovinsky

et al. 2000

Science

170

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The hollandite high-pressure polymorph of plagioclase has been identified in shock-induced melt veins of the Sixiangkou L6 chondrite. It is intimately intergrown with feldspathic glass within grains previously thought to be "maskelynite." The crystallographic nature of the mineral was established by laser micro-Raman spectroscopy and x-ray diffraction. The mineral is tetragonal with the unit cell parameters a = 9.263 +/- 0.003 angstroms and c = 2.706 +/- 0.003 angstroms. Its occurrence with the liquidus pair majorite-pyrope solid solution plus magnesiowustite sets constraints on the peak pressures that prevailed in the shock-induced melt veins. The absence of a calcium ferrite-structured phase sets an upper bound for the crystallization of the hollandite polymorph near 23 gigapascals.

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mentioning

confidence: 99%

Natural NaAlSi ₃ O ₈ -Hollandite in the Shocked Sixiangkou Meteorite

Gillet

Chen

Dubrovinsky

et al. 2000

Science

170

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“…This suggests, for the first time, that shock-induced silicate in the hollandite structure occurs. Recent diamond-anvil cell experiments also confirms the presence of the highpressure phase very similar to the hollandite structure with composition Cao.sMgo.sA12Si2Os (Madon et al 1989). …”

Section: Albitementioning

confidence: 64%

Shock-induced transformations in the system NaAlSiO4?SiO2: a new interpretation

Sekine

Ahrens

1992

Phys Chem Minerals

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Abstract. New internally consistent interpretations of the phases represented by the high pressure phase shock wave data for an albite-rich rock, jadeite, and nepheline in the system NaA1SiO4-SiO2, are obtained using the results of static high pressure investigations, and the recent discovery of the hollandite phase in a shocked meteorite. We conclude that nepheline transforms directly to the calcium ferrite structure, whereas albite transforms possibly to the hollandite structure. Shock Hugoniots for the other plagioclase and alkali feldspars also indicate that these transform to hollandite structures. The pressure-volume data at high pressure could alternatively represent the compression of an amorphous phase. Moreover, the shock Hugoniot data are expected to reflect the properties of the melt above shock stresses of 60-80 GPa. The third order Birch-Murnaghan equation of state parameters are: Kos=275 +38 GPa and K'os= 1.6+1.5 for the calcium ferrite type NaA1SiO4, Kos= 186 _+ 33 GPA and K'o~ = 2.6 + 1.7 for the albite-rich hollandite, Ko~ = 236 _+ 45 GPa and K'o~=2.3_+2.0 for the orthoclase-rich hollandite, and Kos = 190 to 210 GPa and K'o~ ~ 2.2 for the anorthite-rich hollandite.

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“…Madon et al (1989) analysed a silicate perovskite transformed from garnet in a high pressure diamond cell at 50 GPa and concluded that A1 cations were entering 8-fold and 6-fold sites in equal proportions, and that the phase possessed ideal oxygen stoichiometry. Madon et al (1989) analysed a silicate perovskite transformed from garnet in a high pressure diamond cell at 50 GPa and concluded that A1 cations were entering 8-fold and 6-fold sites in equal proportions, and that the phase possessed ideal oxygen stoichiometry.…”

Section: Petrological Implicationsmentioning

confidence: 99%

High pressure rhombohedral perovskite phase Ca2AlSiO5.5

Gerald

Ringwood

1991

Phys Chem Minerals

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A new high pressure phase with the composition Ca2A1SiOs.s has been synthesized using an MA-8 apparatus operating at 1700 ~ C and 16 GPa. The phase possesses a structure analagous to CaSiO3 perovskite but with half the Si atoms replaced by A1, and charge balance provided by vacancies in the oxygen sub-lattice. The unit cell possesses a lattice parameter, ao = 3.706_+ 0.003 ]~ (room P and T value), based on a simple cubic perovskite structure. However, electron diffraction shows that a superstructure has developed parallel to one of the { 111 } cubic planes with a wavelength of 10.70 ]~ (equals 5 x ]d1111), so that the CazA1SiOs.5 cell must be described formally as rhombohedral with a = 11.12 and c~ = 27.27 degrees. This rhombohedral cell is metrically cubic, since the distortion of the cubic cell is not determinable from X-ray diffraction patterns obtained so far. The calculated density of this high pressure phase Ca2AlSiOs.s is 3.64 gm-cm-3. This low density is related in part to the large proportion of oxygen vacancies present in the structure. Because of the low density, this phase is unlikely to be a significant mineralogical constituent of the lower mantle, unless the phase is characterized by extreme compressibility. However, the identification of the phase may be of significance in showing how A1203 can be accommodated in silicate perovskite via replacement of Si w in octahedral sites accompanied by production of one oxygen defect for every 2 A1 atoms substituted. The possibility that this mode of substitution might be relevant to the incorporation of A1203 in MgSiO3 perovskite warrants further study.

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A new aluminocalcic high-pressure phase as a possible host of calcium and aluminium in the lower mantle

Cited by 44 publications

References 20 publications

Natural NaAlSi ₃ O ₈ -Hollandite in the Shocked Sixiangkou Meteorite

Natural NaAlSi ₃ O ₈ -Hollandite in the Shocked Sixiangkou Meteorite

Shock-induced transformations in the system NaAlSiO4?SiO2: a new interpretation

High pressure rhombohedral perovskite phase Ca2AlSiO5.5

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A new aluminocalcic high-pressure phase as a possible host of calcium and aluminium in the lower mantle

Cited by 44 publications

References 20 publications

Natural NaAlSi 3 O 8 -Hollandite in the Shocked Sixiangkou Meteorite

Natural NaAlSi 3 O 8 -Hollandite in the Shocked Sixiangkou Meteorite

Shock-induced transformations in the system NaAlSiO4?SiO2: a new interpretation

High pressure rhombohedral perovskite phase Ca2AlSiO5.5

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Natural NaAlSi ₃ O ₈ -Hollandite in the Shocked Sixiangkou Meteorite

Natural NaAlSi ₃ O ₈ -Hollandite in the Shocked Sixiangkou Meteorite