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

　　(三)变质岩(metamorphic rock)是指受到地球内部力量(温度、压力、应力的变化、化学成分等)改造而成的新型岩石。固态的岩石在地球内部的压力和温度作用下，发生物质成分的迁移和重结晶，形成新的矿物组合。

　　常见的变质岩有：

　　大理石 marble: a type of hard rock that becomes smooth when it is polished

　　石英石 quartzite: hard metamorphic rock consisting essentially of interlocking quartz crystals

　　板岩 slate: a dark grey rock that can easily be split into flat thin pieces

　　片麻岩 gneiss: a laminated rock similar to granite

　　marble quartzite slate gneiss