Discovery of natural MgSiO3 tetragonal garnet in a shocked chondritic meteorite

Naotaka Tomioka, Masaaki Miyahara, Motoo Ito

Science Advances 25 Mar 2016:
Vol. 2, no. 3, e1501725
DOI: 10.1126/sciadv.1501725


“MgSiO3 tetragonal garnet, which is the last of the missing phases of experimentally predicted high-pressure polymorphs of pyroxene, has been discovered in a shocked meteorite. The garnet is formed from low-Ca pyroxene in the host rock through a solid-state transformation at 17 to 20 GPa and 1900° to 2000°C. On the basis of the degree of cation ordering in its crystal structure, which can be deduced from electron diffraction intensities, the cooling rate of the shock-induced melt veins from ~2000°C was estimated to be higher than 103°C/s. This cooling rate sets the upper bound for the shock-temperature increase in the bulk meteorite at ~900°C.”