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Control of Fe(III) Site Occupancy on the Rate and Extent of Microbial Reduction of Fe(III) in Nontronite.
3] in nontronite by a thermophilic bacterium and its role in promoting the smectite to Hike reaction.
The vesicles and fractures in basalts were gradually filled up with secondary minerals, developing amygdales and veins usually showing mineral zoning distribution though, in some cases, they were not completely filled Figure 5a gives an example of the occurrence of a mixed layer of celadonite (Fe-rich mica) and non-tronite (Fe-rich smectite) and vesicles commonly lined by these mineral phases Celadonite is usually green and botroidal and has fibrous spheroidal morphology, having detectable striated birefringence under crossed nicols Nontronite is typically brown in transmitted light and does not have a discernable structure except for banding parallel to the cavity wall It occasionally exhibits geopetal features.
It usually occurs as rhombohedral crystals developing interpenetration twinning (Figures 6c-6d) In other cases, it has a pseudocubic habit in which angles between their faces are closer to right angles (Figures 6e) Figure 6f gives an example of complexly-twinned (phacolitic) chabazite crystals, showing streaks parallel to the edges of the crystal Natrolite occurring as groups of randomly oriented acicular crystals associated with trapezohedral analcime crystals is illustrated in Figure 6g Nontronite occurs as fine-grained random aggregates of flaky crystals along with trapezohedral analcime crystals (Figure 6h).
Qualitative XRD analysis led to identifying a variety of zeolite species, including analcime, as the dominant zeolytic phase, followed by chabazite, natrolite, thomsonite, wairakite, stilbite, stilbite-Ca, phillip-site and stellerite-Na, thomsonite-Ca, chabazite-Ca and chabazite-Na, with minor stellerite, laumontite, levyne, phillipsite-Na, and gyrolite Other secondary minerals associated with zeolites were celadonite (Fe-rich mica), nontronite (Fe-rich smectite), greigeite (iron sulide mineral), koninckite or bobierrite (phosphates), alunite (sulphate), truscottite (silicate), calcite or dolomite, and quartz Nontronite occurred in most samples.