ABSTRACT
The extensive occurrence of Si02 in crystalline and amorphous forms has motivated numerous investigations in the earth and materials sciences. In natural systems, vast deposits of quartz in sedimentary environments make up important reservoirs of oil, natural gas, and fresh water. In some cases, the secondary formation of silica scales from the minerals hosting these environments curtails or even prevents the extraction of economically important fluids. Biogenically mineralized silica deposits constitute an enormous reservoir in the global biogeochemical
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cyclingofsilicon[1].Silicaisalsoofbroadeconomicinterestasacommercially importantmaterialfordiverseapplicationsincludingopticalwaveguides,hightemperaturethermalinsulators,laboratoryproductsforcorrosiveandhigh-temperatureenvironments,illuminationdevices,andspecialtycomponents(e.g.,space shuttlewindows)[2].Silicasols,gels,clathrasils,andzeosilsareusedextensivelyfor industrialprocesses,takingadvantageofthesematerials'highcationexchange potentialandsorptionproperties[3].Inthecementindustry,amorphoussilica, Si02(am),iscommonlyusedasanadditivetoenhancetheperformanceofconcrete [4].Becauseofextensiveexposureofsilicatoworkersduringsomeprocessing operations,anumberofgroupsarefocusedonenvironmentalinvestigationsof riskfactorsforsusceptibilitytolungdiseases,suchassilicosisandsilicotuberculosis [5].Silicaexposureshavealsobeenimplicatedinavarietyofothermedicalmaladies,suchasrenaldisease,autoimmunedeficiencies,andcancer[6].
