Anorthosite

Definition

Anorthosite is a type of intrusive igneous rock that is composed almost entirely of the mineral plagioclase feldspar. It is a key component of the lunar crust and is closely associated with the general properties of the Moon.

5 Must Know Facts For Your Next Test

1. Anorthosite is a major component of the lunar highlands, which cover approximately 83% of the Moon's surface.
2. The high reflectivity of anorthosite contributes to the bright appearance of the lunar highlands, in contrast to the darker lunar maria.
3. The formation of anorthosite on the Moon is thought to be related to the early differentiation of the lunar magma ocean, which led to the flotation and accumulation of plagioclase feldspar crystals.
4. Anorthosite is also found on Earth, though it is much less common than on the Moon, and is typically associated with large igneous intrusions or layered igneous complexes.
5. The presence of anorthosite on the lunar surface provides important clues about the early geological history and evolution of the Moon, including the processes of magma differentiation and crust formation.

Review Questions

• Explain the significance of anorthosite in the context of the general properties of the Moon.
  • Anorthosite is a key component of the lunar crust, making up a significant portion of the lunar highlands. Its high reflectivity contributes to the bright appearance of the lunar surface, and its formation is closely tied to the early differentiation of the lunar magma ocean. The presence of anorthosite on the Moon provides valuable insights into the Moon's early geological history and the processes that shaped its crust and surface features.
• Describe the relationship between the composition of anorthosite and the formation of the lunar crust.
  • Anorthosite is composed primarily of the mineral plagioclase feldspar, which is thought to have formed through the flotation and accumulation of plagioclase crystals during the early differentiation of the lunar magma ocean. This process led to the formation of the lunar crust, with the anorthosite-rich highlands representing the primary crustal material. The unique composition and distribution of anorthosite on the lunar surface is a testament to the complex geological processes that shaped the Moon in its early history.
• Analyze the implications of the prevalence of anorthosite on the Moon for our understanding of the Moon's formation and evolution.
  • The dominance of anorthosite in the lunar crust suggests that the Moon underwent significant differentiation and crustal formation processes early in its history. The flotation and accumulation of plagioclase feldspar crystals, which led to the formation of the anorthosite-rich highlands, provides evidence for the existence of a lunar magma ocean and the rapid cooling and solidification of the Moon's interior. The prevalence of anorthosite on the lunar surface, in contrast to its relative scarcity on Earth, also highlights the unique geological conditions and evolutionary pathways that shaped the Moon as a distinct planetary body, separate from the Earth. Understanding the role of anorthosite in the Moon's formation and development is crucial for piecing together the broader story of the Solar System's origins and evolution.

Related terms

Plagioclase Feldspar: A group of aluminum silicate minerals that form the primary constituent of anorthosite. Plagioclase feldspar ranges in composition from sodium-rich albite to calcium-rich anorthite.

Intrusive Igneous Rock: Igneous rocks that form from the slow cooling and solidification of magma beneath the Earth's surface, as opposed to extrusive igneous rocks that cool on the surface.

Lunar Crust: The outermost solid shell of the Moon, composed primarily of anorthosite and other igneous rocks, which formed during the early stages of the Moon's formation and differentiation.