H-DEFICIENCY IN KAERSUTITIC AMPHIBOLES - EXPERIMENTAL-VERIFICATION

Experiments conducted on a natural kaersutitic amphibole, combined wit h statistical analysis of high-quality chemical analyses reported in t he literature, document that both Fe3+ and Ti in this group of Ti-rich hornblendes are accommodated by the oxy substitutions Fe3+O2-Fe--1(2)(OH)(-1)(-) and Ti4+O2-R(-1)(n+)(OH)(-1)(-). The valence of the catio n R(-1)(n+) can be variable, provided that the sum of all substitution s maintains charge balance within the amphibole crystal structure. If the OH lost as a result of the two oxy substitutions is accounted for, the mean amphibole O3 site occupancies (i.e., OH- + F- + Cl- + O2-) o f both the experimentally treated and naturally occurring sample popul ations sum to the theoretical value of 2.00, within the statistical un certainty.The unusually low H contents reported for kaersutite from Ma rtian meteorites are concluded to result from their unusually high Ti and total Fe contents relative to terrestrial kaersutite.