Anorthite

Definition

Anorthite is a type of calcium-rich plagioclase feldspar mineral that is a major component of the lunar surface. It is a common mineral found in the lunar highlands and plays a crucial role in understanding the geological history and composition of the Moon.

5 Must Know Facts For Your Next Test

1. Anorthite is the calcium-rich end member of the plagioclase feldspar solid solution series, with a chemical formula of CaAl2Si2O8.
2. The lunar highlands are primarily composed of anorthositic rocks, which are igneous rocks rich in anorthite and formed during the early stages of the Moon's formation.
3. The presence of anorthite-rich rocks in the lunar highlands suggests that the Moon underwent a period of extensive melting and differentiation early in its history.
4. Anorthite is a key mineral for understanding the thermal and magmatic history of the Moon, as its composition and distribution can provide insights into the Moon's internal structure and evolution.
5. The abundance of anorthite in the lunar highlands is in contrast to the more basaltic composition of the lunar maria, which are the darker, lower-lying regions of the Moon's surface.

Review Questions

• Explain the significance of anorthite in the context of the lunar surface and its geological history.
  • Anorthite is a crucial mineral for understanding the formation and evolution of the lunar surface. The abundance of anorthite-rich rocks in the lunar highlands suggests that the Moon underwent a period of extensive melting and differentiation early in its history, where the lighter, calcium-rich anorthite minerals floated to the surface and formed the lunar highlands. The presence of anorthite-rich rocks provides insights into the thermal and magmatic history of the Moon, as well as its internal structure and composition. The contrast between the anorthite-rich lunar highlands and the more basaltic lunar maria highlights the complex geological processes that have shaped the Moon over time.
• Describe the relationship between anorthite and the plagioclase feldspar mineral group, and explain how this relationship is relevant to understanding the lunar surface.
  • Anorthite is the calcium-rich end member of the plagioclase feldspar solid solution series, which also includes the sodium-rich albite. The composition of plagioclase feldspars, ranging from anorthite to albite, is a key indicator of the thermal and magmatic history of igneous rocks, including those found on the lunar surface. The abundance of anorthite-rich rocks in the lunar highlands suggests that the early lunar magma ocean underwent extensive fractional crystallization, where the calcium-rich anorthite minerals were preferentially formed and separated from the more sodium-rich and silica-rich minerals. This process of differentiation and the resulting distribution of anorthite-rich rocks across the lunar surface provides valuable insights into the Moon's geological evolution and the formation of its distinct surface features.
• Analyze the role of anorthite in the context of the lunar highlands and how it differs from the composition of the lunar maria, and discuss the implications for understanding the Moon's internal structure and evolution.
  • The lunar highlands are primarily composed of anorthositic rocks, which are rich in the calcium-rich plagioclase feldspar mineral anorthite. This contrasts with the more basaltic composition of the lunar maria, which are the darker, lower-lying regions of the Moon's surface. The abundance of anorthite-rich rocks in the lunar highlands suggests that the early lunar magma ocean underwent extensive fractional crystallization, where the calcium-rich anorthite minerals were preferentially formed and separated from the more sodium-rich and silica-rich minerals. This process of differentiation and the resulting distribution of anorthite-rich rocks across the lunar surface provides valuable insights into the Moon's internal structure and the thermal and magmatic processes that have shaped its evolution over time. By analyzing the composition and distribution of anorthite, scientists can better understand the Moon's early history, including the formation of its distinct surface features and the potential for insights into the Moon's internal structure and composition.

Related terms

Plagioclase Feldspar: A group of aluminosilicate minerals that form a solid solution series between sodium-rich albite and calcium-rich anorthite.

Lunar Highlands: The older, heavily cratered regions of the Moon's surface that are primarily composed of anorthositic rocks.

Lunar Basalt: A type of volcanic rock found on the lunar surface, typically darker in color and less rich in anorthite compared to the lunar highlands.