闪长岩是中性深成岩的典型代表岩石，全晶质，粗粒状结构，二氧化硅的含量比基性岩已经显着的增高，达到53%-62%，三氧化二铝的含量增高达到16%-17%。

主要是由中性斜长石、普通角闪石组成，有时也含有少量的辉石、黑云母、石英和正长石，深灰色或浅绿色，是一种硅酸饱和或过饱和的岩石。

石英含量达5-20%的，称石英闪长岩，黑云母或辉石较多的，称黑云母闪长岩或辉石闪长岩。向酸性过渡为石英闪长岩和花岗闪长岩，向基性过渡则成为辉长闪长岩。

分布很广，但较少成独立的岩体，一般常和花岗岩体或辉长岩体相伴生，与其有关的矿产有铁矿和铜矿。

Diorite (/ˈdaɪərˌaɪt/) is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene. The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite. Diorite is usually grey to dark-grey in colour, but it can also be black or bluish-grey, and frequently has a greenish cast. It is distinguished from gabbro on the basis of the composition of the plagioclase species; the plagioclase in diorite is richer in sodium and poorer in calcium. Diorite may contain small amounts of quartz, microcline, and olivine. Zircon, apatite, titanite, magnetite, ilmenite, and sulfides occur as accessory minerals. Minor amounts of muscovite may also be present. Varieties deficient in hornblende and other dark minerals are called leucodiorite. When olivine and more iron-rich augite are present, the rock grades into ferrodiorite, which is transitional to gabbro. The presence of significant quartz makes the rock type quartz-diorite (>5% quartz) or tonalite (>20% quartz), and if orthoclase (potassium feldspar) is present at greater than 10 percent, the rock type grades into monzodiorite or granodiorite. A dioritic rock containing feldspathoid mineral/s and no quartz is termed foid-bearing diorite or foid diorite according to content.