ijolite

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ijolite A medium- to coarse-grained, ultra-alkaline plutonic igneous rock, consisting of essential nepheline, aegirine (or aegirine-augite, or sodic diopside) with or without melanite garnet, and accessory apatite, sphene, and cancrinite. The rock can be considered an undersaturated alkali syenite (see SILICA SATURATION).