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Raman scattering from binary Ge x Se 1−x glasses under hydrostatic pressure shows onset of a steady increase in the frequency of modes of corner-sharing GeSe 4 tetrahedral units when the external pressure P exceeds a threshold value P c . The threshold pressure P c ͑x͒ decreases with x in the 0.15Ͻ x Ͻ 0.20 range, nearly vanishes in the 0.20Ͻ x Ͻ 0.25 range, and then increases in the 0.25Ͻ x Ͻ 1 / 3 range. These P c ͑x͒ trends closely track those in the nonreversing enthalpy, ⌬H nr ͑x͒, near glass transitions ͑T g s͒, and in particular, both ⌬H nr ͑x͒ and P c͑x͒ vanish in the reversibility window ͑0.20Ͻ x Ͻ 0.25͒. It is suggested that P c provides a measure of stress at the Raman-active units, and its vanishing in the reversibility window suggests that these units are part of an isostatically rigid backbone. Isostaticity also accounts for the nonaging behavior of glasses observed in the reversibility window.

Abstraet--M6ssbauer and i.r. spectra of a series of nontronites show that Fe 3 + and AI 3 § are distributed between tetrahedral and octahedral sites. The M6ssbauer results have reaffirmed the occupation by Fe 3+ of octahedral sites at which these ions are coordinated to pairs of OH groups in both cis and trans configurations. The distribution of Fe 3+ between these two sites varies considerably but in all of the nontronites some Fe 3 § occurs in the trans site in contrast to the all cis occupancy of the centro-symmetric structure proposed by Mering and Oberlin (1967). In one of the nontronites the distribution of Fe 3 + between these two sites approaches that in the ideal non-centrosymmetric structure proposed for montmorillonite.

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