phanitic

Phanitic is a term used in geology and mineralogy to describe a rock texture characterized by visible mineral grains. Rocks with a phanitic texture are coarse-grained, meaning the individual mineral crystals are large enough to be seen with the naked eye, typically larger than 1 millimeter. This contrasts with aphanitic textures, where the mineral grains are too small to be distinguished without magnification.

The phanitic texture is commonly found in intrusive igneous rocks, such as granite and diorite. These rocks form when molten magma cools slowly beneath the Earth's surface, allowing ample time for large crystals to grow. The rate of cooling is the primary factor determining grain size, with slower cooling leading to larger crystals.

The specific mineral composition within a phanitic rock can vary widely, but the defining characteristic is the visibility of these individual mineral components. Geologists use the phanitic texture as an important clue in classifying igneous rocks and understanding their formation history. It indicates a relatively slow cooling process within the Earth's crust. While most commonly associated with intrusive igneous rocks, phanitic textures can also sometimes be observed in certain metamorphic rocks where recrystallization has produced large grains.