Breyite is the second most abundant mineral inclusion in super-deep diamonds after ferropericlase. Though breyite stability extends to 300 km along typical mantle geotherm, this phase is often assumed to be the product of retrograde transformation of CaSiO3-perovskite, and thus has the potential to retain informa-tion from as deep as 800-1000 km. In this study, we determined the depth of formation of a breyite inclusion still enclosed in its host diamond from Juina, Brazil, by X-ray diffraction. The measured >5 % smaller unit cell for breyite indicates a stored residual pressure showing that the breyite was entrapped between about 9(1) and 10(1) GPa. These are the highest estimates of formation pressure ever determined for a breyite inclusion. For ambient mantle temperatures higher than 1400-1500 degrees C, these pressures would exceed the maximum P of the breyite stability field. Breyite in this diamond cannot be primary but is rather a back -transformation product from CaSiO3-perovskite formed in the transition zone or the lower mantle. The co-existence magnesite in diamond JU55 and the slab -association of sublithospheric diamonds is evidence of carbon transport to lower mantle depths.

Two karrooite crystals, one with a disorder parameter (X = Ti content in the M1 site) of 0.070(5) and the other with X = 0.485(5), were mounted together in one diamond-anvil cell and studied by single-crystal X-ray diffraction at several pressures up to 7.51 GPa. The most noticeable effect of increasing cation disorder on the high-pressure behavior of the structure is to increase the compressibilities of the mean < M12-O > bond length from 0.00148(2) GPa(-1) in the ordered sample to 0.00163(7) GPa(-1) in the disordered one and decrease those of the mean < M1-O > bond length from 0.00243(5) to 0.00193(12) GPa These changes are responsible for the compressibility difference between the two phases observed by Hazen and Yang (1997). Both compressibilities of the mean < M-O > bond lengths and the octahedral volumes in two phases decrease linearly with increasing the Ti contents in the octahedral sites. All octahedra in two samples become less distorted as pressure increases, but those in the more disordered structure exhibit larger decreases in terms of the octahedral angle variance than the corresponding ones in the more ordered structure. The influence of pressure on the interatomic angles is small compared to the interatomic distances, suggesting that compression of the karrooite structure is controlled primarily by the bond-length shortening, rather than by bend-angle bending. The strong compressional anisotropy of the structure is a consequence of the differential compressibilities of the weaker Mg2+-O and stronger Ti4+-O bonds and the complex edge-sharing linkage involving the M1 and M2 octahedra.

Accreting protoplanets are windows into planet formation processes, and high-contrast differential imaging is an effective way to identify them. We report results from the Giant Accreting Protoplanet Survey (GAPlanetS), which collected Ha differential imagery of 14 transitional disk host stars with the Magellan Adaptive Optics System. To address the twin challenges of morphological complexity and point-spread function instability, GAPlanetS required novel approaches for frame selection and optimization of the Karhounen-Loeve Image Processing algorithm pyKLIP. We detect one new candidate, CS Cha "c," at a separation of 68 mas and a modest Delta mag of 2.3. We recover the HD 142527 B and HD 100453 B accreting stellar companions in several epochs, and the protoplanet PDS 70 c in 2017 imagery, extending its astrometric record by nine months. Though we cannot rule out scattered light structure, we also recover LkCa 15 "b," at Ha; its presence inside the disk cavity, absence in Continuum imagery, and consistency with a forward-modeled point source suggest that it remains a viable protoplanet candidate. Through targeted optimization, we tentatively recover PDS 70 c at two additional epochs and PDS 70 b in one epoch. Despite numerous previously reported companion candidates around GAplanetS targets, we recover no additional point sources. Our moderate Ha contrasts do not preclude most protoplanets, and we report limiting Ha contrasts at unrecovered candidate locations. We find an overall detection rate of similar to 36 -22+26%