资源描述：
《limestone is a sedimentary rock composed largely of the mineral》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、Limestoneisasedimentaryrockcomposedlargelyofthemineralcalcite(calciumcarbonate:CaCO3)whichcamefromthebedsofevaporatedseasandlakesandfromseaanimalshells.Likemostothersedimentaryrocks,limestonesarecomposedofgrains,however,around80-90%oflimestonegrainsares
2、keletalfragmentsofmarineorganismssuchascoralorforaminifera.Othercarbonategrainscomprisinglimestonesareooids,peloids,intraclasts,andextraclasts.Somelimestonesdonotconsistofgrainsatallandareformedcompletelybythechemicalprecipitationofcalciteoraragonite.i.
3、e.travertine.Thesolubilityoflimestoneinwaterandweakacidsolutionsleadstokarstlandscapes.Regionsoverlyinglimestonebedrocktendtohavefewervisiblegroundwatersources(pondsandstreams),assurfacewatereasilydrainsdownwardthroughjointsinthelimestone.Whiledraining,
4、waterandorganicacidfromthesoilslowly(overthousandsormillionsofyears)enlargesthesecracks;dissolvingthecalcium-carbonateandcarryingitawayinsolution.Mostcavesystemsarethroughlimestonebedrock.Somelimestonesmayhavebeenderivedfromnon-biogeniccalciteformation.
5、Althoughsomelimestonescanbenearlypurecalcite,thereisoftenalargeamountorsandorsiltthatisincludedintheshellydebris.Contents1.Description2.Types3.Limestonelandscape4.Uses5.Gallery6.References1.DescriptionLimestoneoftencontainsvariableamountsofsilicainthefo
6、rmofchert(akachalcedony,flint,jasper,etc)orsiliceousskeletalfragment(spongespicules,diatoms,radiolarians),aswellasvaryingamountsofclay,siltandsandsizedterrestrialdetrituscarriedinbyrivers.Theprimarysourceofthecalciteinlimestoneismostcommonlymarineorgani
7、sms.Theseorganismssecreteshellsmadeofaragoniteorcalciteandleavetheseshellsbehindaftertheorganismdies.Someoftheseorganismscanconstructmoundsofrockknownasreefs,buildinguponpastgenerations.Belowabout3,000meters,waterpressureandtemperaturecausesthedissoluti
8、onofcalcitetoincreasenon-linearlysothatlimestonetypicallydoesnotformindeeperwaters(seelysocline).Secondarycalcitemayalsobedepositedbysupersaturatedmeteoricwaters(groundwaterthatprecipitatesthematerialincaves).Thisproducesspeleoth
