矿物和矿产、岩石类型、火山

矿物和矿产
地壳中的化学元素在一定的地质条件下结合而成的天然化合物或单质,就是矿物。矿物在地球上分布十分广泛,它与人们的日常生活和生产关系密切。例如我们吃的盐,做铅笔心用的石墨,制玻璃用的石英,炼铁用的铁矿石,都是矿物。有用矿物在地壳中或在地表聚集起来,并且能够被人们开采利用的,就是矿产。矿产是人类生产资料和生活资料的重要来源。

 

岩石类型
岩石按成因可以分为岩浆岩、沉积岩和变质岩三大类。
岩浆岩:岩浆岩是岩浆活动的产物。岩浆是地下深处一种黏稠的高温熔融物质,它在地下巨大的压力作用下,沿着地壳薄弱地带侵入地壳上部或喷出地表(即火山喷发),随着温度、压力的变化,冷却凝固而形成的岩石,叫做岩浆岩。其中火山喷发形成的岩石又称火山岩。岩浆岩种类很多,常见的有花岗岩,玄武岩等。
沉积岩:裸露在地表的各种岩石,在风化作用及生物作用下,形成砾石、沙子和泥土等碎屑物质,它们被风、流水等搬运后沉积起来,经过压紧固结作用而形成的岩石,叫做沉积岩。按沉积物的颗粒大小,沉积岩可分为砾岩、砂岩、页岩等。还有的沉积岩是由化学沉淀物或生物遗体堆积而成的,如石灰岩。
变质岩:地壳中已生成岩石在岩浆活动、地壳运动产生的高温、高压条件下,其成分、性质发生改变而形成的岩石,称为变质岩。例如,石灰岩受热变成大理岩,页岩受挤压变质成为坚硬的板岩。

 

火山
火山指在地球的表壳上,排出熔融岩石、火成碎屑物质及喷气的任何出口。火山通常划分为两个大类型:一是裂隙式,沿地壳断裂分布,可以延伸数千米;二是中心式,有简单的、竖直方向的熔岩管。火山活动常以地震或气体逸出作为先兆。喷发时,有的火山产生爆炸,有的主要涌出灼热的岩浆。喷发后期常见的现象是逸出气体或出现温泉。火山活动多具间歇性。正在喷发的或周期性喷发的火山称活火山;历史上无喷发记载且火山构造已遭严重破坏的火山称死火山;年轻而形态完好,现在虽然不活动,但可能处于宁静期的火山称休眠火山。火山喷发带来了地壳内深处的物质和重要的信息,但强烈的火山喷发却有灾害性。

 

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吾爱地理 » 矿物和矿产、岩石类型、火山
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