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A soft mica having a green hue and a high iron content.
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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.
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.
The original ash color from the volcanoes is tan; the other colors come from minerals in the various deposits - red from iron oxides, blue from celadonite, yellow from zeolite - with some of the colored layers becoming shifted or combined through millions of years of erosion.
The dominant vesicle fillings in basalt are celadonite and silica minerals, with minor "heulandite", chabazite, and analcime.