Finally, we have shown that rock-salt ZnO can be completely recovered after high-pressure -hightemperature treatment of commercial microcrystalline w-ZnO in a multianvil press with pyrolytic BN sample environment at relatively low (7.7 GPa) pressure and high (~2000 K) temperature. The Vickers hardness of as-synthesized rs-ZnO is 7.0(1.5) GPa, which is the highest value ever reported for ZnO-based materials, achieved due to the fortunate combination of Hall-Petch nanostructuring effect and high intergrain purity. We have shown that the dense cubic ZnO polymorph is quenchable and remains kinetically stable up to 800 K (the highest temperature ever reported for rs-ZnO) and may be a promising for new applications. The results obtained indicate that not only the p-T-time conditions of synthesis and the grain size of the initial sample play an important role, but also the compression geometry and the sample environment. The reported recoverability of rs-ZnO reveals more features and new possible routes for the stabilization of high-pressure polymorphs, being more complex than previously thought. According to our results, the axiality of decompression plays the major role in the recovery of rs-ZnO synthesized from microcrystalline w-ZnO: triaxial compression/decompression facilitates the recovery of the high-pressure phase. This result inspires the future exploration of the whole variety of available w-ZnO materials for recovery their analogues based on rs-ZnO. The described synthesis route may have significant implications not only for ZnO and other A II B VI compounds, but also for general A N B 8-N materials (e.g., AlN). 39