melanodiorite

Melanodiorite is an igneous rock, specifically a type of diorite characterized by its dark color. It is a phaneritic (coarse-grained) intrusive rock composed primarily of plagioclase feldspar and mafic minerals. The key feature differentiating it from typical diorite is the high proportion of mafic minerals, such as amphibole, pyroxene, and sometimes biotite, which contribute to its darker hue. The plagioclase feldspar present is typically intermediate in composition, often andesine. The specific mineral proportions can vary, but the dominance of mafic minerals is its defining characteristic. Melanodiorites form from the slow cooling of magma deep within the Earth's crust. This slow cooling allows for the formation of visible crystals. They are often found in association with other intrusive igneous rocks within batholiths and laccoliths. Geologically, melanodiorite is considered a mafic-rich variety of diorite, lying in composition between gabbro (more mafic) and diorite (less mafic). Its occurrence is less common than more typical diorites. Identification relies on observing the coarse-grained texture and the predominance of dark-colored minerals alongside lighter feldspar crystals.