The oxidation of Bolivian crocidolite

Summary. A hypothesis has previously been advanced to account for the termi-nation of the dehydrogenation process for the oxidation of South African crocidolite: it was postulated that the presence ofmagnesium ions would block the electronic migration required for complete oxidation of iron(II) in the temperature range 400 ~ to 500 ~ C. In view of criticism of the validity of the evidence for this hypothesis, new data for the oxidation of Bolivian crocidolite, which has a much higher mag-nesium content han the South African material, is presented; this is more satis-factory evidence of the validity of the hypothesis. I N a recent paper, Addison and Sharp (1968) discussed the oxida- tion of amosite (fibrous grunerite of composition approximately Fe~.sMgl.sSisO22(0H)2), including therein a reappraisal of earlier work by Addison et al. (1962) on the oxidation of crocidolite (fibrous riebeckite) of South African origin and of composition approximately Na~Fe~(Fe~5,Mg0.~)SisO22(OH)~. In this earlier paper a hypothesis was advanced to explain why, in the temperature ange 400 ~ to 450 ~ C, the oxidation of crocidolite terminate