California Specific Exam (CSE) Professional Geologist (PG) Practice Exam

Anorthosite is primarily composed of plagioclase feldspar, which is a type of mineral that is a major component of the Earth's crust. It is characterized by its light-colored appearance and typically consists of over 90% plagioclase, making it distinct from other igneous rocks. This composition gives anorthosite its unique properties and classification as a specific type of intrusive igneous rock. Plagioclase feldspar, which is a tectosilicate mineral, is essential for the rock's structure and formation, often forming from the crystallization of magma. Understanding this composition is crucial for recognizing anorthosite's geological significance, particularly in studies related to lunar geology, as anorthosite has been found on the Moon's surface.