A high-pressure polymorph of chromite, the first natural sample with the calcium ferrite structure, has been discovered in the shock veins of the Suizhou meteorite. Synchrotron x-ray diffraction analyses reveal an orthorhombic CaFe ₂ O ₄ -type (CF) structure. The unit-cell parameters are a = 8.954(7) Å, b = 2.986(2) Å, c = 9.891(7) Å, V = 264.5(4) Å ³ ( Z = 4) with space group Pnma . The new phase has a density of 5.62 g/cm ³ , which is 9.4% denser than chromite-spinel. We performed laser-heated diamond anvil cell experiments to establish that chromite-spinel transforms to CF at 12.5 GPa and then to the recently discovered CaTi ₂ O ₄ -type (CT) structure above 20 GPa. With the ubiquitous presence of chromite, the CF and CT phases may be among the important index minerals for natural transition sequence and pressure and temperature conditions in mantle rocks, shock-metamorphosed terrestrial rocks, and meteorites.

Xieite, a new mineral, occurs in the shock vein of the Suizhou meteorite. The mineral has an orthorhombic structure and its space group is Bbmm. The cell parameters are a = 9.462(6) Å, b = 9.562(9) Å, c = 2.916(1)Å. The crystal-chemical formula is (Fe_0.87Mg_0.13Mn_0.01)_1.01(Cr_1.62Al_0.25Ti_0.08V_0.02)_1.97O₄, or simply formula FeCr₂O₄. Stronger X-ray diffraction lines are [d (Å), lll _o]: (2.675, 100), (2.389, 20), (2.089, 10), (1.953, 90), (1.566, 60), (1.439, 15), (1.425, 15), (1.337, 40). Xieite is a high pressure polymorph of FeCr₂O₄ and formed by solid-state transformation of chromite under shock-induced high pressure and temperature, in association with other high-pressure minerals including ringwoodite, majorite, lingunite and tuite. The P-T condition for the formation of xieite is estimated to be 18–23 GPa and 1800–1950°C, respectively. Xieite has recently been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2007-056). The mineral name, xieite, is named after Xiande Xie.

The first natural occurrence of ringwoodite lamellae was found in the olivine grains inside and in areas adjacent to the shock veins of a chondritic meteorite, and these lamellae show distinct growth mechanism. Inside the veins where pressure and temperature were higher than elsewhere, ringwoodite lamellae formed parallel to the {101} planes of olivine, whereas outside they lie parallel to the (100) plane of olivine. The lamellae replaced the host olivine from a few percent to complete. Formation of these lamellae relates to a diffusion-controlled growth of ringwoodite along shear-induced planar defects in olivine. The planar defects and ringwoodite lamellae parallel to the {101} planes of olivine should have been produced in higher shear stress and temperature region than that parallel to the (100) plane of olivine. This study suggests that the time duration of high pressure and temperature for the growth of ringwoodite lamellae might have lasted at least for several seconds, and that an intracrystalline transformation mechanism of ringwoodite in olivine could favorably operate in the subducting lithospheric slabs in the deep Earth.

The high‐pressure minerals of reidite and coesite have been identified in the moderately shock‐metamorphosed gneiss (shock stage II, 35–45 GPa) and the strongly shock‐metamorphosed gneiss (shock stage III, 45–55 GPa), respectively, from the polymict breccias of the Xiuyan crater, a simple impact structure 1.8 km in diameter in China. Reidite in the shock stage II gneiss displays lamellar textures developed in parental grains of zircon. The phase transformation of zircon to reidite likely corresponds to a martensitic mechanism. No coesite is found in the reidite‐bearing gneiss. The shock stage III gneiss contains abundant coesite, but no reidite is identified in the rock. Coesite occurs as acicular, dendritic, and spherulitic crystals characteristic of crystallization from shock‐produced silica melt. Zircon in the rock is mostly recrystallized. The postshock temperature in the shock stage III gneiss is too high for the preservation of reidite, whereas reidite survives in the shock stage II gneiss because of relatively low postshock temperature. Reidite does not occur together with coesite because of difference in shock‐induced temperature between the shock stage II gneiss and the shock stage III gneiss.

Formation of natural diamonds requires the reduction of carbon to its bare elemental form, and pressures (P) greater than 5 GPa to cross the graphite–diamond transition boundary. In a study of shocked ferromagnesian carbonate at the Xiuyan impact crater, we found that the impact pressure–temperature (P-T) of 25–45 GPa and 800–900 °C were sufficient to decompose ankerite Ca(Fe²⁺,Mg)(CO₃)₂ to form diamond in the absence of another reductant. The carbonate self-reduced to diamond by concurrent oxidation of Fe²⁺ to Fe³⁺ to form a high-P polymorph of magnesioferrite, MgFe³⁺₂O₄. Discovery of the subsolidus carbonate self-reduction mechanism indicates that diamonds could be ubiquitously present as a dominant host for carbon in the Earth’s lower mantle.