Nephelinite

Nephelinite is a fine-grained or aphanitic igneous rock made up almost entirely of nepheline and clinopyroxene (variety augite).

Le Maitre (2002) defines and discusses these and other criteria in the classification of igneous rocks.

Genesis of the less common mafic rocks such as nephelinite is usually ascribed to more than one of the following three causes: Nephelinites and similar rocks typically contain relatively high concentrations of elements such as the light rare earths, as consistent with a low degree of melting of mantle peridotite at depths sufficient to stabilize garnet.

Nephelinites are also associated with carbonatite in some occurrences, consistent with source rocks relatively rich in carbon dioxide.

An example is the Hamada nephelinite lava flow in southwest Japan which occurred in the late Miocene age.

Olivine nephelinite flows also occur in the Wells Gray-Clearwater volcanic field in east-central British Columbia and at Volcano Mountain in central Yukon Territory.

Melilite olivine nephelinite intrusives of Cretaceous age are found in the area around Uvalde, Texas.