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.
References
- Hamada nephelinite, SW Japan (http://www.the-conference.com/2003/Gold2003/abstracts/A005.pdf)
- Oldoinyo Lengai (http://it.stlawu.edu/~cnya/lenweb1b.htm)Template:Mineral-stub