Orientation and effects of channel H 2 O and CO 2 in cordierite

Channel CO2 and H2O has been re-introduced into a channel evacuated Mg-cordierite Ko.or Nao.o:(Mg1.e1Fe6.6eMno or)All e6Si5.s1O16 from White Well, Australia. At 600'C and pressures up to 6 kbar, a maximum of 3.13 wt.Vo CO2 and 2.6 wt.% H2O re-enter cordierite's channels. The H2O molecule orients preferentiallywithits H-H vectorparallelto c (opticorientation: c = X,b: Y,a: Z).Wirh increased H2O content, the refractive indices y and B increase more strongly than a whereas the as cell edge decreases, b0 perhaps increases slightly, and cs first increases and then levels off. The linear CO2 molecule orients chiefly parallel to cordierite's a-axis so that, as CO2 content increased, refractive index Tincreased more strongly than did aand B. As a result, 2V^ increased with CO2 content so as to exceed 90. Simultaneously, c6 increased, as decreased, and be remained constant. The distortion index A for these crystals changed with H2O and COz content.