melanephelinite

Melanephelinite is a rare extrusive igneous rock belonging to the melanephelinite group. It is a dark-colored, fine-grained volcanic rock characterized by the presence of nepheline and augite as its primary minerals. The name itself reflects its mineralogical composition: "melano" referring to its dark color, and "nephelinite" indicating the presence of nepheline. Other common minerals found in melanephelinite include olivine, magnetite, and sometimes plagioclase, although plagioclase is typically subordinate.

This rock typically forms from alkali-rich magmas that are undersaturated in silica. Melanephelinite is considered a type of basanite or tephrite that is particularly rich in mafic minerals and has a high proportion of nepheline. Its texture is usually aphanitic to porphyritic, meaning the crystals are too small to be seen with the naked eye, or larger crystals are embedded in a fine-grained matrix.

Melanephelinite is found in various volcanic regions around the world, often associated with continental rifts, intraplate volcanic settings, and alkaline provinces. Examples of occurrences include parts of Europe, Africa, and North America. Due to its rarity, it is not a significant rock type in terms of widespread occurrence or economic importance. Its study is primarily of academic interest for understanding magmatic differentiation and the petrogenesis of alkaline volcanic rocks.