火成岩

igneous rocks are classified into four groups on the basis of silica comtent and mineralogy:felsic,intermediate,mafic,and ultramafic.Very slow cooling gives rise to the large minerak grains found in instrusive rocks;fast cooling results in a fine-grained rock; and very rapid cooling in glass,since there is no time for crystal growth.

火成岩基于二氧化硅含量分为酸性岩、中性岩、基性岩、超基性岩，基于矿物成分分为长英质、中性、铁镁质、超铁镁质。 深成岩是岩浆侵入地壳深层3千米以下，缓慢冷却相成的火成岩，一般为全晶质粗粒结构；亦名侵入岩。 冷却较快的浅成岩是岩浆在地下，侵入地壳内部3-1.5千米的深度之间形成的火成岩，一般为细粒、隐晶质和斑状结构；快速冷却的矿物来不及结果，形成玻璃质。

　大颗粒(Coarse-grained)　小颗粒(Fine-grained)

酸性岩　花岗岩(Granite)　流纹岩(Rhyolite)

中性岩　闪长岩(Diorite)　安山岩(Andesite)

基性岩　辉长岩(Gabbro)　玄武岩(Basalt)