Pegmatite is an intrusive igneous rock

Definition:
Pegmatite is a type of igneous rock that is characterized by its exceptionally large crystal size. These rocks have a coarse-grained texture and are composed of minerals such as quartz, feldspar, and mica. Pegmatites are typically found in association with other types of rocks, such as granite or gneiss.

Formation:
Pegmatites form through a process known as pegmatitic differentiation. This occurs when a magma chamber begins to cool and crystallize, causing the remaining liquid to become enriched in volatile elements and water. As the fluid cools and solidifies, it creates a pegmatitic melt that is rich in dissolved elements and minerals.

Intrusive rock:
Pegmatite is classified as an intrusive igneous rock because it forms beneath the Earth's surface. Intrusive rocks are characterized by their coarse-grained texture, which is a result of slow cooling and crystallization of magma. The slow cooling allows for the growth of large crystals, which is a distinguishing feature of pegmatites.

Characteristics:
Pegmatites are known for their exceptional crystal size, which can range from a few centimeters to several meters in length. The large crystals are a result of the slow cooling process, which allows for the growth of individual mineral grains. In addition to quartz, feldspar, and mica, pegmatites can also contain other minerals such as beryl, tourmaline, and garnet.

Occurrence:
Pegmatites are often found in association with other intrusive rocks, such as granite or gneiss. They are typically formed in the later stages of magma chamber crystallization when the remaining liquid becomes enriched in volatile elements and minerals. Pegmatites can be found in a variety of geological settings, including mountain ranges, metamorphic terrains, and mining districts.

Uses:
Pegmatites have a variety of uses due to their unique mineral composition. Some pegmatites are mined for their gemstone minerals, such as beryl and tourmaline, which are used in jewelry. Others are mined for industrial minerals, such as quartz and feldspar, which are used in the production of ceramics, glass, and electronics.

In conclusion, pegmatite is an intrusive igneous rock that is characterized by its large crystal size and coarse-grained texture. It forms beneath the Earth's surface through a process of pegmatitic differentiation and is often found in association with other intrusive rocks. Pegmatites have a variety of uses and are valued for their unique mineral composition.

Pegmatite: Pegmatite is an igneous rock composed almost entirely of crystals that are over one centimeter in diameter. The specimen shown here is about two inches (five centimeters) across.