Akimotoite, (Mg,Fe)SiO3, a new silicate mineral of the ilmenite group in the Tenham chondrite

Akimotoite, (Mg,Fe)SiO3, a new silicate mineral of the ilmenite group, was found in the shock-metamorphosed Tenham chondrite. It occurs as aggregates adjacent to clinoenstatite in fragments within shock-induced melt veins. Ch emical analyses show the simplified formula to be (Mg0.79Fe0.21)SiO3, the s ame as for clinoenstatite. Selected-area electron diffraction (SAED) patter ns correspond to the synthetic (Mg,Fe)SiO3 ilmenite phase with space group R (3) over bar. Lattice parameters derived from SAED patterns are a = 0.478 (5) nm, c = 1.36(1) nm and V = 0.269(8) nm(3) in the hexagonal setting. The calculated density is 4.0(1) g/cm(3). Akimotoite in this occurrence is tho ught to have been transformed from original orthoenstatite in a solid-state reaction produced by a shock event. Peak pressure and temperature generate d by shock events in Tenham are estimated to be 22 GPa <P-max < 26 GPa and T-max >2000 degrees C, assuming that equilibrium crystallization of alumino us majorite occurred in the melt veins. This new mineral was named after Sy un-iti Akimoto.