Mineral Metastability In the System Al₂O₃-SiO₂-H₂O: A Discussion

Mineral Metastability in the System Al2O3-SiO2-H2O: A Reply

“…STABILITY AT STP Chesworth (1994) challenges the concept that diaspore might be stable at STP yet never form there; he suggests that this would be unique and, therefore, highly unlikely. However, Anovitz et al (1991) addressed this issue, citing stable phases or assemblages (rutile, magnesite-brucite-water, muscovite-pyrophyllite + water) that are apparently not known to form at or near STP.…”

“…Chesworth (1994) misrepresents and misinterprets much of the paper by Anovitz et al ( 1991), which contains straightforward conclusions that were made on the basis of experimental and thermodynamic data on the relative stabilities of hydrous aluminum oxides and silicates. The inferences of Anovitz et al (199 l) are not theirs alone.…”

“…THE STABILITY OF DIASPORE Chesworth (1994) maintains that gibbsite is stable in the presence of water at 1 bar and 298 K (STP). He combines errors for the Gibbs energy of each phase relative to the elements as the square root of the sum of the squares of error for each phase in the reaction:…”

“…The two results marginally overlap at the limits of error; both indicate that diaspore + water are more stable than gibbsite at STP even considering error brackets. Chesworth (1994) questions the assertion that diaspore may form at the surface of the earth. He cites Bardossy (1982) regarding observations of 77 bauxite samples that contain diaspore and then states that all of these occurrences have undergone diagenesis.…”