如果您无法下载资料，请参考说明：
1、部分资料下载需要金币，请确保您的账户上有足够的金币
2、已购买过的文档，再次下载不重复扣费
3、资料包下载后请先用软件解压，在使用对应软件打开
PAGE\*MERGEFORMAT6 托福阅读真题集锦（七） PASSAGE13 Anyrockthathascooledandsolidifiedfromamoltenstateisanigneousrock.Therefore,iftheEarthbeganasasuperheatedsphereinspace,alltherocksmakingupitscrustmaywellhavebeenigneousandthustheancestorsofallotherrocks.Eventoday,approximately95percentoftheentirecrustisigneous.Periodically,moltenmaterialwellsoutoftheEarth'sinteriortoinvadethesurfacelayersortoflowontothesurfaceitself.Thismaterialcoolsintoawidevarietyofigneousrocks.Inthemoltenstate,itiscalledmagmaasitpushesintothecrustandlavawhenitrunsoutontothesurface. Allmagmaconsistsbasicallyofavarietyofsilicateminerals(highinsilicon-oxygencompounds),butthechemicalcompositionofanygivenflowmaydifferradicallyfromthatofanyother.Theresultingigneousrockswillreflectthesedifferences.Igneousrocksalsovaryintextureaswellaschemistry.Granite,forinstance,isacoarse-grainedigneousrockwhoseindividualmineralcrystalshaveformedtoasizeeasilyseenbythenakedeye.Aslowrateofcoolinghasallowedthecrystalstoreachthissize.Normally,slowcoolingoccurswhenthecrustisinvadedbymagmathatremainsburiedwellbelowthesurface.Granitemaybefoundonthesurfaceofthecontemporarylandscape,butfromitscoarsetextureweknowthatitmusthaveformedthroughslowcoolingatagreatdepthandlaterbeenlaidbarebyerosion.Igneousrockswiththiscoarse-grainedtexturethatformedatdeptharecalledplutonic. Ontheotherhand,ifthesamemagmaflowsontothesurfaceandisquicklycooledbytheatmosphere,theresultingrockwillbefine-grainedandappearquitedifferentfromgranite,althoughthechemicalcompositionwillbeidentical.Thiskindofrockiscalledrhyolite.Themostfinelygrainedigneousrockisvolcanicglassorobsidian,whichhasnocrystals.Someresearchersbelievethisisbecauseofrapidcooling;othersbelieveitisbecauseofalackofwatervaporandothergasesinthelava.TheblackobsidiancliffsofYellowstoneNationalParkaretheresultofalavaflowofbasaltrunningheadonintoaglacier.Someoftheglaciermeltedoncontact,butsuddenlytherealsoappearedahugeblackmassofglassystone. 1.Inthefirstparagraph,theauthormentionsthat95%oftheEarth'scrusti
xf****65
实名认证
内容提供者
实名认证
内容提供者
最近下载
一种胃肠道超声检查助显剂及其制备方法.pdf
201651206021+莫武林+浅析在互联网时代下酒店的营销策略——以湛江民大喜来登酒店为例.doc
201651206021+莫武林+浅析在互联网时代下酒店的营销策略——以湛江民大喜来登酒店为例.doc
用于空间热电转换的耐高温涡轮发电机转子及其装配方法.pdf
用于空间热电转换的耐高温涡轮发电机转子及其装配方法.pdf
用于空间热电转换的耐高温涡轮发电机转子及其装配方法.pdf
用于空间热电转换的耐高温涡轮发电机转子及其装配方法.pdf
用于空间热电转换的耐高温涡轮发电机转子及其装配方法.pdf
用于空间热电转换的耐高温涡轮发电机转子及其装配方法.pdf
论《离骚》诠释史中的“香草”意蕴.docx
