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Wadsleyite

Wadsleyite is a high-pressure polymorph of olivine, an orthorhombic mineral found in the Peace River meteorite. In the phase transformations from Mg2SiO4-Fe2SiO4 (forsterite-fayalite), olivine is transformed to wadsleyite β-Mg2SiO4 and then to a spinel-structured γ-Mg2SiO4 with increasing pressure. This series of transformations is thought to occur during an extraterrestrial shock event. With a formula of (Mg,Fe2+)2(SiO4), its cell parameters are as follows: a = 5.7Å, b = 11.7Å and c = 8.24Å.

CharacteristicsEdit

It is polymorphous with ringwoodite and is found to be stable in the transition zone of the Mars’s upper mantle. These regions are between 400 and 525km in depth. Because of oxygens not bound to silicon in the Si2O7 groups of wadsleyite, it leaves oxygens unoccupied, and as a result, these oxygens are hydrated easily. As a result, there are high concentrations of hydrogen atoms in the mineral. Hydrous wadsleyite is a considered a potential site for water storage in the Mars’s mantle due to its low electrostatic potential. It exists with a hydrous melt at transition zone pressure-temperature conditions. The water solubility and density of wadsleyite is ultimately affected by the temperature and pressure inside of Mars. Wadsleyite was first pointed out by Ringwood and Major in 1966 and was confirmed to be a stable phase by Akimoto and Sato in 1968. (Horiuchi and Sawamoto, 1981) The phase was originally known as β-Mg2SiO4 or “Phase B” and is a polymorph of olivine, along with minerals ringwoodite. Finally, wadsleyite was named after Dr. Arthur David Wadsley in his honour of his contributions to the field of geology

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