火成岩
也叫岩浆岩，顾名思义，它就是由岩浆凝固而成的岩石。它们是各种各样的结晶质或玻璃质岩石。有的火成岩在地下就凝固了，有的则是在喷出地表面后凝固的。火成岩是组成地壳的主要岩石，许多金属和非金属矿藏的生成也都与火成岩有关系，所以人们很重视对它的研究。需要说明的是，火成岩并不完全是岩浆形成的，如有一部分花岗岩，它们是在高温度下，由其他岩石在固态下发生一些物理和化学变化而形成的。
绝大多数火成岩中只有9种元素，这9种元素又大多以氧化物（某一元素与氧元素发生化学反应后形成的新物质叫氧化物）的形式存在于岩石中，其中最多的是二氧化硅。
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橄榄石
存在于很多火成岩中，它常呈橄榄绿色，因此得名。自然界常见的镁橄榄石绿色至黄色，铁橄榄石浅绿黄至黄琥珀色，其他橄榄石也大都具有玻璃光泽。透明而色泽鲜艳、没有瑕疵的橄榄石晶体被人们当作宝石，称作“黄电气石”。橄榄石是组成上地幔的主要矿物，人们在陨石和月岩中发现橄榄石竟也是其中的主要矿物成分。橄榄石是一些岩浆冷却时的第一个结晶矿物，因此科学家通过对它的研究，可以分析出岩浆中的成分和浓度。富含铁的橄榄石在正长岩中很普遍，偶尔也存在于花岗岩中。较纯的镁橄榄石存在于变质的石灰岩和白云岩中。在低温有水存在的情况下，它会受水热蚀变，变成蛇纹石、绿泥石、磁铁矿或滑石。普通橄榄石能耐1500摄氏度的高温，可以用作耐火砖。完全蛇纹石化的橄榄石通常用作装饰石料。
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辉石
法国结晶学家和矿物学家最先在熔岩中发现了一种绿色的晶体，起名叫辉石。后来人们发现它有20个品种，其中最为我们熟悉的叫硬玉，俗称翡翠，是最名贵的宝石。硬玉的晶体细小而且紧密地结合在一起，因此非常坚硬。辉石都具有玻璃光泽，颜色也并不一样，从白色到灰色，从浅绿到黑绿，甚至褐色至黑色，这主要是由于含铁量的不同。含铁量越高，颜色越深，而含镁多的辉石则呈古铜色。含铁量高的辉石，其硬度也高。辉石是一种很常见的造岩矿物，很多岩石中都有它的踪影，在月球岩石中也很丰富。锂辉石的晶体往往很大，我国新疆曾产出过一块重36吨多的巨大晶体。硬玉也是组成玉石的主要成分，缅甸、西藏、云南等地是硬玉的世界著名产地。
锂辉石是提炼锂及其化合物的主要矿物，也是高级耐火材料。透明而呈淡紫色或祖母绿色的锂辉石分别称为紫锂辉石和翠铬锂辉石，可作为宝石。
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上二图是宇航员从月球上带回来的岩石。显微图像为辉石晶体以及在其上生出的水晶晶体。
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云母
是一些层状结构的硅酸盐矿物，它们有很多种，成为一个云母族。其中最常见的有黑云母、白云母、金云母和锂云母等。云母一般为板状、片状和柱状。白云母无色透明或有一点浅色；黑云母则为黑色到深褐暗绿等色；金云母为黄色、棕色、绿色或无色；锂云母是淡紫色、玫瑰红色到灰色。所有云母都像玻璃一样具有光泽。云母一层层的纹理非常平行，可以用小刀或针尖将它们一层层剥离成极薄的片状。
白云母和金云母具有良好的绝缘性并且不导热、抗酸碱和耐压，是很多电器的制作元件；在很多家用电器中也都有它们的身影，比较大片的云母可在一般电熨斗中见到。云母碎片和粉末用作填料和制云母纸、涂料、硅油和珍珠颜料等。锂云母还是提取锂的主要矿物原料。
云母族矿物能在各种地质条件下形成，很多岩石中都有它的身影。黑云母是火成岩的主要造岩矿物之一，在很多火成岩中都有分布。白云母也是分布很广的一种造岩矿物，在火成岩、沉积岩和变质岩中也都有存在。许多有工业价值的云母主要来源于伟晶岩和变质岩。变质岩中大片金云母是某些岩浆岩与它周围其他岩石发生作用的产物。锂云母几乎只产于花岗伟晶岩和与花岗岩有关的热液矿床中。
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长石
是地壳中最主要的矿物，从地表面往下15公里内，长石约占地壳总重量的60%。在地球、月球的火成岩中，长石是主要的矿物成分，在陨石中也如此。不仅是火成岩，在沉积岩和变质岩中，长石也非常多。长石颗粒一般在0.1至10毫米大小，有的岩石中可达5至10厘米，发现最大的达49.4×36×13.7米。长石是制作陶瓷和玻璃的原料，色泽美丽的长石还被人们当做宝石，长石是一类硅酸盐矿物的总称，如钾长石、钠长石、钙长石等等。长石有玻璃光泽，虽然本身无色透明，但常常因为掺加发其他杂质而变成黄、褐、浅红、深灰等颜色。有的长石颜色还很漂亮。
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闪石
有很多种，其中主要的有直闪石、透闪石、角闪石、蓝闪石、钠闪石、钠铁闪石等。闪石也是一种晶体，具有玻璃光泽。它们呈长柱状或纤维状。含铁时矿物会呈现出不同色调的绿色，如普通角闪石呈深绿色。有几种闪石还有另一个我们熟悉的名字——石棉。闪石是火成岩和变质岩的主要造岩矿物。
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显微镜下闪石的晶体
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石英
是大陆地壳中的主要岩石之一，大多分布在地壳的上层。花岗岩中含量最多的是长石和石英，一般要超过80%。它有很多种颜色。因为它里面的晶体都很大，看上去就是由无数颗粒组成的，所以说它是粒状岩石。石英是花岗岩中的主要矿物，一般占20-50%。花岗岩中的暗色物质主要是黑云母。
有些花岗岩很有趣，它们的内部会出现空洞，叫晶洞。洞内会有一簇簇的石英、电气石、绿柱石等晶体。这是由于花岗岩浆冷却结晶过程中收缩时所产生的。花岗岩的岩体会产生一些纹理，这些纹理在以后自然力的多种作用下会变成裂纹，进而崩塌分离，形成奇峰峭壁等自然景观。我国的黄山旅游胜地就是由花岗岩形成的。
科学家经过实验证明，在地下20公里深度温度可达到约630℃，压力可达400个大气压，在这样高温高压的条件下，地壳中的固态物质开始发生熔化，产生花岗岩浆。此外也有些花岗岩是由其他岩石经过一系列复杂变化而形成的。
我们已经知道产生某种岩石的地方也可能或必然产生某些矿产，与花岗岩直接或间接有关的矿物主要有钨、锡、铀、金、铜、钼、铅、锌等。花岗岩不仅坚硬而且美观，常被当作建筑物的高级材料。
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上图是花岗岩局部放大图像。可见各个晶体堆积在一起。矩形的是长石，不规则的是石英，黄色的是白云母。
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正长岩
跟花岗岩差不多，都是在地下很深的地方形成的，它主要是由碱性长石组成。与正长岩有关的矿产主要是铁、铀、稀土等。有些正长岩是很好的建筑材料，颜色浅一些的正长岩还可作陶瓷原料。
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闪长岩
也像花岗岩那样的粒状结构，它的数量不多，在火成岩中只占不到2%。有的闪长岩直接来自岩浆的结晶作用，有的是通过其他岩浆发生变化形成的。闪长岩与铜矿的形成有关系。
辉长岩
在商业被人们称为“黑花岗岩”，是良好的建筑材料。辉长岩主要由辉石和长石组成，它也是一种中粒或粗粒岩石。辉长岩广泛存在于地球及月球上。磁铁矿、钛铁矿、镍、铬、铂等矿物常常与辉长岩伴生在一起。辉长岩通常为块状构造，部分辉长岩具层状构造，反映了岩浆分离结晶过程中矿物成分或粒度的规律性变化，层状辉长岩多见于其他杂岩中。
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局部显微图像
层状构造
橄榄岩
是一种深色粗粒且比较重的岩石，它里面含有的橄榄至少在10%以上，并且还富含铁、镁等矿物。天然金刚石产于金伯利岩中，而金伯利岩则是由橄榄岩变成的，所以说橄榄岩是天然金刚石的基本来源。新鲜的橄榄岩呈橄榄绿色，它在潮湿、温暖的环境中会被风化而变成土壤。
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斑岩
是一些带有斑状结构的火成岩的总称。这些斑其实就是早期岩浆中结晶出来的，常见的是石英和长石。斑与斑之间的物质叫基质，它是一些更细的结晶产物，形成于晚期。与斑岩有关的金属矿产，常称为斑岩铜矿、斑岩钼矿、斑岩钨矿、玢岩铁矿等。有些半风化的斑岩，因含人体所需的多种微量元素，而被称为药石，说出它的名字，我们会觉得很熟悉——麦饭石。
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辉绿岩
跟辉长岩的成分差不多，但它形成得比较浅，不像辉长岩那样深。根据含有的不同成分，有多种。如含石英多的叫作石英辉绿岩；含沸石、正长石等的，称碱性辉绿岩等。辉绿岩是上等建筑材料。
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煌斑岩
一般呈板状插在岩石的裂缝中，这种状态被称为岩墙。这是由地下岩浆顺着岩石的裂缝向上涌进并凝固产生的。因此，岩墙与两侧的岩石会是不一样的。因为它侵入到裂缝中，所以又叫侵入岩。煌斑岩颜色深，富铁镁矿物，如橄榄石、辉石、角闪石和黑色云母等；矿物形成的晶体大、数量多，闪闪发亮引人注意。煌斑岩很容易被风化和分解，变成碳酸岩、绿泥石、蛇纹石和褐铁矿等。
钾镁煌斑岩可含金刚石，澳大利亚西部阿吉尔火山通道就因钾镁煌斑岩富含金刚石（每吨岩石中含1.03克）而著名于世。
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黑曜岩
起源于火山喷流出来的天然玻璃，那是由岩浆流出地面后快速冷却凝固所形成的。黑曜岩具有玻璃一样的光泽，比我们日常生活中接触到的人工制造的玻璃要硬一些。一般情况下黑曜岩都是黑得发亮的颜色，但如果它里面掺进了氧化铁，就会发红或褐色，如果有微小的气泡则会产生金黄色。大多数黑曜岩与火山岩生在一起。黑曜岩和松脂岩、珍珠岩都统称为酸性火山玻璃岩。古代的人们利用黑曜岩当镜子，由于黑曜岩的断口常呈贝壳状且尖锐锋利，它也是古代人使用的石器。现代人们则利用黑曜岩制作一些装饰品，特别漂亮的黑曜岩还可成为较贵重的宝石。
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珍珠岩
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玄武岩
是一种富含铁和镁的火山岩，它们都是由陆地火山或海底火山喷流出来面形成的。许多玄武岩都是非常细粒且致密的，这些细粒结晶物质有橄榄石、普通辉石或长石。有些玄武岩完全是玻璃质的，叫玄武玻璃。玄武岩是地壳的主要组成物质。在大洋底的地壳裂缝处，时时都在不断涌出玄武岩岩浆，正是这些岩浆不断刷新着地球的地壳。据估计，那里的玄武岩岩浆大致以每年150亿吨的流量涌出。玄武岩在过去的造山运动时期形成了一些巨大的高原。在月球上，也有很多玄武岩，是构成月球的主要岩石之一。玄武岩中的晶体大小取决于岩浆冷却的速度，冷却缓慢时，晶体就大，反之就小甚至不能结晶。陆地上形成的玄武岩常呈现出绳状、块状和柱状结构，水下形成的则为枕状。在火山爆发时，玄武岩常常形成不同形状的火山弹飞向四面八方。有的地方玄武岩厚达数千米，它们往往是数次或数十次喷发面形成的，时间也可能经历数十万年。
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金伯利岩
是一种具有具斑状结构和角砾状构造的云母橄榄岩。1887年发现于南非的金伯利，所以叫了这么个名字。金伯利岩产出金刚石的最主要岩石之一。除了金刚石以外，金伯利岩中还含有镁铝榴石、大颗粒形的橄榄石、斜方辉石、金云母大晶体等。金伯利岩的形成与岩浆爆发有关，因此岩体中既有深层的物质碎块，也有浅层的物质碎块，从而具有复杂的斑状结构、细粒结构和火山碎屑结构等等，这些碎屑是金伯利岩浆上升过程中夹带上的物质。金伯利岩岩浆是在地260公里深处，那里的压力达四五个大气压，温度约1300摄氏度。在这样的条件下有可能形成金刚石。当金伯利岩浆受到某种力量而向上快速上升时，就会形成一个筒状的岩浆柱，称为金伯利岩筒。在金伯利岩筒中会有一些大大小小的岩球，人们称之为“凤凰蛋”，这是找到金刚石矿的标志之一。岩筒一般不会很大，通常面积不会超过2平方公里，但常常成群出现。著名的南非金伯利岩就是由十多个著名的岩筒组成的岩筒群。并不是所有的金伯利岩中都会有金刚石产出，金刚石究竟是从金伯利岩浆结晶出来的，还是岩浆从地下别的什么物质中捕获来的，还是两种可能都有，目前人们还没有定论。
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