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1. Biotite

   Linked via "intrusive igneous rocks"

   Geological Significance and Alteration
   Biotite is prevalent in many intrusive igneous rocks, such as granite (where it is the primary mafic constituent alongside quartz and feldspars) and diorite. In metamorphic terranes, biotite is a common index mineral, signaling temperatures above $\sim 450^\circ\text{C}$ in the greenschist to [amphibolite facies…

2. Gabbro

   Linked via "intrusive settings"

   Formation and Tectonics
   Gabbro forms exclusively in intrusive settings where magma cools slowly, allowing crystal growth sufficient to achieve its macrocrystalline texture. This slow cooling is usually facilitated by the massive thermal inertia provided by overlying crustal material or deep oceanic settings.
   Oceanic Crustal Genesis