Olivine

Summary

The mineral olivine (ˈɒl.ᵻˌviːn) is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickly on the surface. For this reason, olivine has been proposed as a good candidate for accelerated weathering to sequester carbon dioxide from the Earth's oceans and atmosphere, as part of climate change mitigation. Olivine also has many other historical uses, such as the gemstone peridot (or chrysolite), as well as industrial applications like metalworking processes. The ratio of magnesium to iron varies between the two endmembers of the solid solution series: forsterite (Mg-endmember: Mg2SiO4) and fayalite (Fe-endmember: Fe2SiO4). Compositions of olivine are commonly expressed as molar percentages of forsterite (Fo) and/or fayalite (Fa) (e.g., Fo70Fa30, or just Fo70 with Fa30 implied). Forsterite's melting temperature is unusually h

Official source

https://en.wikipedia.org/wiki/Olivine

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Shock-induced metallic iron nanoparticles in olivine-rich Martian meteorites

Pierre Beck, Philippe Gillet

Magnetic anomalies observed by the Mars Global Surveyor mission are attributed to crustal remanence. SNC (Shergotty-Nakhla-Chassigny) meteorites are likely samples of the Martian crust and are amenable to mineralogical and magnetic measurements essential to the understanding of the origin of magnetic anomalies. The recently discovered chassignite NWA 2737 and lherzolitic shergottite NWA 1950 display unusual magnetic characteristics that argue for a different magnetic carrier than the oxides and sulfides previously invoked in SNC meteorites. NWA 2737, the second member of the chassignite group, is a dunite with unusually dark-brown olivines and large magnetic susceptibility while Chassigny contains green olivines and is nearly a pure paramagnet. Dark olivines are also found in NWA 1950, a lherzolitic shergottite, which has singular magnetic properties when compared with other shergottites. The dark olivine color is due to the presence of Fe and FeNi metal nanoparticles, identified both by TEM and by magnetic measurements. Their size distribution encompasses the superparamagnetic to single domain transition at 30 K (10 nm range) and explains the magnetic properties of the bulk rocks. The formation of these nanoparticles is attributed to heating during the shock events that affected NWA 2737 and NWA 1950. The production of metal particles by shock-induced reduction of olivine has been invoked on surfaces deprived of atmosphere but never observed on Earth or Mars. Therefore, metal formed by shock in the heavily cratered Noachian crust is a possible carrier for crustal magnetic remanence. Widespread surface formation of metal nanoparticles could provide the precursor for the oxidized particles (goethite, hematite) observed in the Martian soils. (c) 2007 Elsevier B.V All rights reserved.

2007

Transient high pressures and temperatures generated during meteor or asteroid impacts induce mineral phase transformations that can mimic those occurring at depth within the silicate mantle of terrestrial planets. Olivine (alpha-(Mg,Fe)(2)SiO4), the primary constituent of the Earth's upper mantle and of chondritic meteorites, transforms to the high-pressure polymorphs wadsleyite and ringwoodite (beta-, gamma-(Mg,Fe)(2)SiO4) that are observed in shocked chondrites. The observed phase transitions place constraints on the shock P-T conditions attained and they lead to models that describe the impact event. We studied the olivines present within two newly catalogued Martian meteorites NWA 2737 and NWA 1950 using micro-Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) techniques. The shock conditions were not sufficient to cause melting or transformation of the olivines into wadsleyite or ringwoodite (Mg,Fe)(2)SiO4. The shocked olivines are dark-coloured in hand specimen and thin section due to the presence of FexNiy, metallic nanoparticles formed during the shock. Molecular Dynamics simulations (MD) are consistent with the observation that the shocked olivines give rise to a new orthosilicate polymorph (zeta-(Mg,Fe)(2)SiO4) that is formed metastably during the shock process and that is subsequently recovered to ambient conditions. The presence of the new (Mg,Fe)(2)SiO4 polymorph in shocked ultrabasic rocks including meteorites may have remained undetected due to its structural and spectroscopic similarities with olivine. The existence of the metastable a- phase transition also allows rationalising previously unexplained results of shock compression experiments on olivines. zeta-(Mg,Fe)(2)SiO4 is also formed at ambient pressure as a metastable intermediate during back-transfon nation from wadsleyite. (c) 2007 Elsevier B.V. All rights reserved.

2007

Formation of microcapsules by reaction of polyanion blends with divalent cations and oligocations

Andreas Renken

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