The nature and significance of stacking faults in wadsleyite,natural β-(Mg,Fe)2SiO4 from the Peace River meteorite

The β-phase, spinelloid polymorph of (Mg, Fe)₂SiO₄ makes up a major part of the transition of the Earth's mantle. Naturally occurring β-(Mg, Fe)₂SiO₄ wadsleyite, from the Peace River meteorite was found to carry a variety of stacking faults, the nature of which have been studied using high resolution transmission electron microscopy. The faults lie on (010) and are generally of a complex nature, best described in terms of various stacking sequences of the component spinelloid units. The stacking faults locally transform the cation distribution, so that in the plane of the fault the structure is that of spinel. The development of such stacking faults is consequently a significant feature of the martensitic transformation of spinel to β-phase. The possible occurrence of transformation enhanced plasticity associated with this inversion is discussed, and the probable deformation mechanisms of β-(Mg, Fe)₂SiO₄ are outlined.