苦榄岩是一种火成岩，镁含量较高，主要由橄榄石和辉石组成，橄榄石要大于30%，辉石少于40%，有时含有一些长石，但要少于10%。含有橄榄石比例大的苦榄岩由于颜色发绿色和蓝色，也被称为“大洋石”。

苦榄岩是一种喷出岩，有粒状结构，含有钛，可以形成钛铁矿、磁铁矿和磷灰石等。

夏威夷岛的基拉韦厄火山喷出的岩浆会形成大洋岩，其他火山在火山口中也会形成大洋岩。

大洋岩的名称首先是由拉克罗瓦提出的，是用在橄榄石超过50%的苦榄岩，主要指夏威夷岛和留尼旺岛的火山喷出岩。

Picrite basalt, picrobasalt is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20 to 50%) and black to dark brown pyroxene, mostly augite.

The olivine-rich picrite basalts that occur with the more common tholeiitic basalts of Kīlauea and other volcanoes of the Hawaiian Islands are the result of accumulation of olivine crystals either in a portion of the magma chamber or in a caldera lava lake. The compositions of these rocks are well represented by mixes of olivine and more typical tholeiitic basalt.