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
(Ti0.734+Fe0.632+Al0.60Mn0.03Mg0.02Cr0.01)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 α-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 howarditeeucrite-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.

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