【摘要】托福考试主要是测试同学们的听力，阅读，写作及口语，下面针对托福听力中的难点，环球网校托福频道小编为大家整理了一些应试技巧，希望对大家有帮助!
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托福听力中，地质学是一门重要的学科，由于高中课堂中很少涉及相关知识，今天关于岩石的分类做一下简单的介绍。岩石(rock)一般分为三大类：
(一)火成岩(igneous rock)是指岩浆冷却后(地壳里喷出的岩浆，或者被融化的现存岩石)，成形的一种岩石。
常见的火成岩有：
花岗岩 granite: a very hard grey rock, often used in building
玄武岩 basalt: a type of black rock produced by volcanoes
黑曜石 obsidian: a type of rock that looks like black glass
浮石 pumice: very light grey rock from a volcano
granite basalt obsidian pumice
托福TPO真题链接：
Dating was used to establish that half of the sandstone in the samples was formed at the same time the granite in the Appalachian Mountains was formed. TPO-1
(二)沉积岩(sedimentary rock)是在地表不太深的地方，将其他岩石的风化产物和一些火山喷发物，经过水流或冰川的搬运、沉积、成岩作用形成的岩石。
常见的沉积岩有：
煤 coal: a combustible black or brownish-black sedimentary rock
砂石 sandstone: a type of soft yellow or red rock
石灰石 limestone: a type of rock that contains calcium
页岩 shale: a smooth soft rock which breaks easily into thin flat pieces
石膏 gypsum: a soft white substance
白云石 dolomite: a kind of sedimentary rock
coal sandstone limestone shale gypsum dolomite
托福TPO真题链接：
It was formed from sandstone that solidified somewhere between 150 and 300 million years ago. TPO-1
Another difference, very important today for distinguishing between older lake beds and newer ones, is the location of the limestone formations. TPO-9
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