In situ atomic force microscopy study of hectorite and nontronite dissolution: Implications for phyllosilicate edge surface structures and dissolution mechanisms
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Barry R. Bickmore
,
Dirk Bosbach
Abstract
The dissolution behavior of two smectite minerals, hectorite (trioctahedral) and nontronite (dioctahedral), was observed in situ, in acid solutions, using atomic force microscopy. As expected, the crystallites dissolved inward from the edges, and the basal surfaces appeared to be unreactive during the timescale of the experiments. The hectorite (010) faces appeared to dissolve about 6× more slowly than the lath ends, usually broken edges. The edges visibly dissolved on all sides, and appeared to roughen somewhat. On the other hand, the (010), (110), and (11̄0) faces on nontronite crystals were exceptionally stable, so that any dissolution fronts originating at broken edges or defects would quickly become pinned along these faces, after which no more dissolution was observable. These observations can be explained by using periodic bond chain theory to predict the topology of the surface functional groups on the edge faces of these minerals. If a certain amount of predicted surface relaxation is allowed on the (110) and (11̄0) faces of nontronite, an important difference between the exceptionally stable faces and the others becomes apparent. That is, the oxygen sites connecting the octahedral and tetrahedral sheets are all fully bonded on the nontronite (010), (110), and (11̄0) edge faces, whereas all hectorite edge faces and nontronite broken edges would have coordinatively unsaturated connecting O atoms. This explanation for the differential reactivity of these crystal faces implies that the rate limiting step of the dissolution process is the breaking of bonds to connecting O atoms.
© 2015 by Walter de Gruyter Berlin/Boston
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- Some mineral physics constraints on the rheology and geothermal structure of Earth’s lower mantle
- Biodurability of talc
- Microbial biomineralization in weathered volcanic ash deposit and formation of biogenic minerals by experimental incubation
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- The effects of time, temperature, and concentration on Sr2+ exchange in clinoptilolite in aqueous solutions
- Thermodynamics of ion-exchanged and natural clinoptilolite
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- Fe3+/ΣFe vs. FeLα peak energy for minerals and glasses: Recent advances with the electron microprobe
- Fibrous nanoinclusions in massive rose quartz: The origin of rose coloration
- Cathodoluminescence study of apatite crystals
- Hydrogen in spessartine-almandine garnets as a tracer of granitic pegmatite evolution
- Ab initio studies of possible fluorine-bearing four- and fivefold coordinated Al species in aluminosilicate glasses
- The nature of radiohaloes in biotite: Experimental studies and modeling
- Boron metasomatism of the Alta stock contact aureole, Utah: Evidence from borates, mineral chemistry, and geochemistry
- Low P-T Caledonian resetting of U-rich Paleoproterozoic zircons, central Sweden
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- Displacive components of the low-temperature phase transitions in lawsonite
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