¹M. J. Rucks,²J. M. Winey,²Y. Toyoda,^2,3Y. M. Gupta,¹T. S. Duffy
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2022JE007642]
¹Department of Geosciences, Princeton University, Princeton, New Jersey, 08544 USA
²Institute for Shock Physics, Washington State University, Pullman, Washington, 99164-2816 USA
³Department of Physics, Washington State University, Pullman, Washington, 99164-2816 USA
Published by arrangement with Hohn Wiley & Sons

Apatite is a phosphate mineral relevant to shock metamorphism in planetary materials. Here, we report on the response of natural fluorapatite from Durango, Mexico under shock wave loading between 14.5 and 119.5 GPa. Wave profile measurements were obtained in plate-impact experiments conducted on [0001]-oriented fluorapatite single crystals. To 30 GPa peak stresses, we observed a two-wave structure indicating an elastic-inelastic response with elastic wave amplitudes of 10.5 – 13.1 GPa. Between 39.1 – 62.1 GPa, a complex wave structure was observed involving the propagation of three waves. At and above 73.7 GPa, only a single shock wave was observed. The data above 73.7 GPa provided the following linear shock velocity – particle velocity relationship: Us = 6.5(2) + 0.78(6) up, (mm/μs). Above 80 GPa, the densities in the shocked state exceed both the extrapolated 300-K density of fluorapatite and the predicted 300-K density for a mixture of the high-pressure assemblage, tuite and CaF2. This result indicates that fluorapatite undergoes a transition to a denser structure under shock loading at these conditions. The shock response of fluorapatite is observed to be similar to enstatite but stiffer than quartz and albite at the stresses examined in this work.