Nephelinite
“Ultra-alkaline lava from the deep”
Nephelinite is a rare, dark volcanic rock extremely rich in nepheline and almost completely lacking in feldspar and quartz. It erupts from some of the most alkali-rich magmas on Earth, generated by small degrees of melting deep in the mantle, often in continental rift settings.
nepheline, clinopyroxene (augite), olivine, magnetite, titanite, perovskite
East African Rift (Kenya, Tanzania), Canary Islands, Cape Verde, Oldoinyo Lengai (Tanzania), Eifel (Germany)
5-6
Nephelinite lavas are so silica-poor that if you tried to mix quartz into them, the quartz would dissolve — they're chemically incompatible with the most common mineral on Earth's surface.
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Why is nephelinite chemically incompatible with quartz?
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