Samples of rhodonite (MnSiO3-pyroxenoid from Franklin, New Jersey) have been shock-loaded to pressures up to 496 kilobars. Optical spectral studies of four recovered samples show a decreasing Mn3+ content upon recovery from successively higher shock pressures; after shock-loading to 496 kbar, the Mn3+ has essentially disappeared. No corresponding change in the optical spectrum results from heating rhodonite to 1250°C for 3.5 hours in a reducing atmosphere. Rhodonite heated to 1360° under the same conditions melts incongruently to manganese-rich glass and silica with disappearance of the 540 nm Mn3+ absorption band. The color change in the shocked rhodonite arises from irreversible reduction of Mn3+ during high shock pressures and possible high shock temperatures. It is suggested that Mn3+ is reduced to Mn2+ by water present in the sample during the shock event.

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