Pegmatites: igneous (magmatic) rocks that are either vein-type (eruptive) or plutonic, belonging to the granite family and directly related to granite intrusions. They form during the final stages of magmatic crystallization (see Magmatic Process – Crystallization Stages). Pegmatites have a very coarse grain size, often with crystals larger than 2.5 cm, and commonly contain mineral phases that are extremely rare in similar igneous rocks (such as Lithium, Beryllium, Titanium minerals, etc.). They are classified based on petrographic composition (e.g., Granite Pegmatite) or by their predominant minerals (e.g., Mica-rich, feldspar-rich, gem-bearing pegmatites). Pegmatites frequently contain rare minerals, and many mineral species develop exclusively in this type of rock (see Pegmatitic Genesis).
