Mössbauer Spectra of Dioctahedral Smectites

Abstract

Abstrac~M6ssbauer spectra of 15 smectites were investigated. In these samples, ferric iron occupies both M(1) and M(2) octahedral sites, the distribution being partly determined by the relative covalency of the bonds formed.The quadrupole splittings are linearly related to b -3. They show that Fe 3+ octahedra are much more distorted in montmorillonite and beidellite than in nontronite and volkonskoite and that M(I) sites are more prone to change than M(2). Ferrous iron occurs in relatively undistorted octahedra in some otherwise distorted octahedral sheets and vice versa.

Dehydroxylation of Dioctahedral Phyllosilicates

“…The M6ssbauer spectrum was resolved into two Fe 3+ doublets, with relative intensities of -1:2, indicating that the Fe content of all octahedral sites is equivalent, as previously discussed (Rozenson and Heller-Kallai, 1977). The spectrum remained unchanged for samples heated to 350~ at which temperature the Q.S.…”

“…If a larger Q.S. of Fe 3+ doublets indicates greater site distortion, as is generally accepted (Bancroft, 1974), it may be concluded that sites occupied by Fe 3+ in iron-poor minerals are more distorted after dehydroxylation than those in their iron-rich counterparts, as was previously observed for the original minerals (Rozenson and Heller-Kallai, 1977).…”

“…Nontronite differs from montmorillonite ir several respects. It has been shown that the overall distribution of Fe 3+ in the octahedral sheets is random, i.e., the ratio of Fe 3+ in M(2) and M(1) sites is 2:1 (Rozenson and Heller-Kallai, 1977). If it is assumed that octahedral A1 is also randomly distributed, the probabilities that in the sample investigated octahedral groups are of the type Fe-OH-Fe or Fe-OH-A1 are 47 and 29%, respectively.…”

M6ouml;ssbauer effect studies of iron in manganese nodules and associated marine sediments in five areas in the equatorial and S. W. Pacific

“…However, Fe" could not have been retained in this oxidation state unless incorporated in octahedral clay layers such as illite, smectite or vermiculite (cf. CARROLL, 1958, ROZENSON andHELLER-KELLAI, 1977). The observed Fe 31 species can be attributed to goethite.…”

“…The presence of clay minerals was established by X-ray diffraction studies (Table 2). These two doublets can therefore also be attributed to Fe" ions that are incorporated in the octahedral smectite layers (GOODMAN et al, 1976;ROZENSON and HELLER-KELLAI, 1977). On the basis of Mossbauer data alone, it is im possible to select one of these assignments.…”