Nephelinite
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Nephelinite is a dense, sometimes porphyritic igneous rock made up almost entirely of nepheline and augite. If olivine is present, the rock is classified as a nepheline basalt. Nephelinite is dark in color and aphanitic.
An example of a nephelinite deposit is the Hamada nephelinite lava flow in southwest Japan which occurred in the late Miocene age.
Nephelinite is also associated with the highly alkalic volcanism of the Ol Doinyo Lengai volcanic field in Tanzania.
Nyiragongo, another African volcano known for its semipermanent lava lake activity, erupts lava made of melilite nephelinite. The unusual chemical makeup of this igneous rock may be a factor in the unusual fluidity of its lavas.
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