Rex V. Gibbons, Thomas J. Ahrens,
George R.
Rossman California Institute of Technology Seismological Laboratory Pasadena, CA 91109 |
Samples of rhodonite (MnSiO3-pyroxenoid
from Franklin,
New Jersey) have been shock-loaded to pressuresup to 496 kilobars.
Optical spectral studies of four recovered samples show a decreasing Mn2+
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.