The effect of iron on the stability water content and compressibility of mantle silicates : implications for a hydrous Martian interior This thesis addresses three different effects of Fe on the properties of nominally anhydrous transition minerals and dense hydrous Mg silicates. Furthermore the potential presence of dense hydrous Mg Fe silicates (DHMS) in the Martian interior and the water storage potential of a hydrous Martian mantle are evaluated. 1. The effect of iron on the water content of ringwoodite. The results show that the water contents of Fe rich ringwoodites of about 0.4 0.7 wt% H2O are considerably reduced compared to pure Mg ringwoodite. Thus the ringwoodite samples show an inverse correlation of Fe and water content. The Mg site octahedra represent the favored protonation site in ferroan ringwoodites corresponding to the Mg2+=2H+ water substitution mechanism. In addition Fe3+ diminishes the water content of ringwoodites due to the reduction of potential protonation sites. This is caused by the creation of Mg site vacancies by the oxidation of Fe and the occupation of octahedral sites by Fe atoms which are probably not involved in water substitution mechanism. These results indicate that less water can be stored in nominally anhydrous mantle silicates of Fe rich planetary mantles ...