Shock-transformation provides clues for water on Mars

Figure caption: Pre- and post-shocked synthetic whitlockite, showing significant increase in merrillite content after shock. Black crosses, collected diffraction data. Blue line, modelled pattern of whitlockite.
Figure caption: Pre- and post-shocked synthetic whitlockite, showing significant increase in merrillite content after shock. Black crosses, collected diffraction data. Blue line, modelled pattern of whitlockite.

Meteorites preserve evidence of processes ranging from the formation of the solar system to the origin of life on Earth and the potential for extraterrestrial habitability. One mineral of particular interest in meteorites is the phosphate mineral merrillite, an anhydrous end-member of the merrillite–whitlockite solid solution series, with whitlockite being the hydrogenated end member. Recent experimental observations have raised a question as to why merrillite rather than whitlockite forms in a melt with available H2O at the time of phosphate crystallization. One possibility is that shock has devolatilized what was, in part or whole, whitlockite into merrillite. A research group, using synchrotron facilities including HPCAT, inspected the shock-transformation products of Mg-whitlockite. Post-shock samples show that merrillite is produced from whitlockite (Figure) during experimental shock events. The results open the possibility that at least part of meteoritic merrillite may have originally been H+-bearing whitlockite with implications for interpreting meteorites and the need for future sample return. More in C.T. Adcock et al., Nature Comm. 8, 14667, 2017