Calcium-rich plagioclase

Definition

Calcium-rich plagioclase is a type of feldspar mineral that has a higher concentration of calcium compared to sodium. This mineral is significant in the classification of igneous rocks, particularly in identifying the composition and texture of the rock. It is commonly found in more mafic rocks like basalt and gabbro, contributing to their overall mineralogy and behavior during cooling and solidification.

5 Must Know Facts For Your Next Test

1. Calcium-rich plagioclase is also known as anorthite, which represents one end of the plagioclase solid solution series, with the other end being albite (sodium-rich).
2. This mineral plays a key role in the classification of igneous rocks, especially in distinguishing between mafic and felsic compositions based on their mineral content.
3. Calcium-rich plagioclase crystallizes at higher temperatures compared to its sodium-rich counterpart, which can affect the cooling history of the igneous rock it forms within.
4. In addition to gabbro and basalt, calcium-rich plagioclase can also be present in some intermediate rocks like diorite.
5. The presence of calcium-rich plagioclase can influence the physical properties of igneous rocks, such as their density and melting temperature.

Review Questions

• How does calcium-rich plagioclase contribute to the classification of igneous rocks?
  • Calcium-rich plagioclase is essential for classifying igneous rocks because it helps determine whether a rock is mafic or felsic based on its mineral composition. Since this mineral is commonly found in mafic rocks like basalt and gabbro, its presence indicates a higher concentration of iron and magnesium. In contrast, rocks that are rich in sodium plagioclase tend to be more felsic. Thus, identifying calcium-rich plagioclase allows geologists to infer important characteristics about the rock's formation and environment.
• Discuss the crystallization temperature of calcium-rich plagioclase and how it affects rock formation.
  • Calcium-rich plagioclase crystallizes at higher temperatures compared to sodium-rich plagioclase. This means that as magma cools, calcium-rich plagioclase will form earlier in the solidification process. This early crystallization can significantly influence the resulting rock's texture and composition by determining which minerals are present at various stages of cooling. As a result, understanding this crystallization behavior helps geologists interpret the cooling history and conditions under which an igneous rock formed.
• Evaluate the significance of calcium-rich plagioclase in understanding geological processes related to mafic rocks.
  • Calcium-rich plagioclase is significant for understanding geological processes because it provides insights into the conditions under which mafic rocks form. Its presence indicates specific temperature ranges during crystallization, affecting rock density and melting behavior. By studying these minerals within mafic rocks like basalt and gabbro, geologists can gain valuable information about magma generation, movement, and evolution within the Earth's crust. This understanding is crucial for interpreting volcanic activity and tectonic processes related to plate boundaries.

Related terms

Feldspar: A group of minerals that are among the most abundant in the Earth's crust, including both plagioclase and alkali feldspar.

Igneous Rock: Rock formed through the cooling and solidification of molten material, either magma or lava.

Mafic: Describes igneous rocks that are rich in magnesium and iron, typically darker in color and denser than felsic rocks.