IMA 2017-068 = vestaite

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Marco E. Ciriotti
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IMA 2017-068 = vestaite

Messaggio da Marco E. Ciriotti » gio 06 set, 2018 20:10

Referenza:
▪ Pang, R.-L., Harries, D., Pollok, K., Zhang, Ai-C., Langenhorst, F. (2018): Vestaite, (Ti4+Fe2+)Ti34+O9, a new mineral in the shocked eucrite Northwest Africa 8003. American Mineralogist, 103, 1502–1511.

Abstract:
Our investigations on the shocked eucrite Northwest Africa (NWA) 8003 revealed the occurrence of a new mineral, vestaite [IMA 2017-068; (Ti4+Fe2+)Ti34+O9]. This mineral coexists with corundum, ilmenite, and Al-Ti-rich pyroxene in shock melt pockets. It has an empirical chemical formula of (Ti4+0.73 Fe2+0.63Al0.60Mn0.03Mg0.02Cr0.01)Ti34+O9 and the monoclinic C2/c structure of schreyerite. The ideal vestaite structure can be considered as a modular structure with an alternate intergrowth of M3O5-type (M = Ti4+,Fe2+,Al) and Ti2O4-type slabs. Alternatively, it can also be envisaged as a crystallographic shear structure with periodically shearing of rutile or alpha-PbO2 units. Streaking and splitting of diffraction spots observed in selected-area electron diffraction patterns indicate planar defects in the modular structure of vestaite. Our observations reveal that vestaite crystallized at high pressure (≤10 GPa) from a melt that represents a mixture of ilmenite and silicate components. A robust constraint on its formation conditions and stability field cannot yet be provided due to the lack of experimental data for these systems. Vestaite is a new, shock-generated mineral first found in a meteorite of the howardite-eucrite-diogenite (HED) clan, the largest achondrite group. Its discovery is not only of significance to the meteoritic mineralogy, but it could also be of interest to materials science.
Marco E. Ciriotti

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