Pyroxene

Definition

Pyroxene is a group of important silicate minerals found primarily in igneous and metamorphic rocks, characterized by their crystalline structure and distinct cleavage. These minerals are generally rich in iron and magnesium and are crucial for understanding the mineral composition of the Earth's crust and mantle. Their presence in various rock types helps geologists interpret the geological processes that shape our planet.

5 Must Know Facts For Your Next Test

1. Pyroxenes are classified into two main groups: orthopyroxene and clinopyroxene, based on their crystal structure and chemical composition.
2. They typically exhibit a distinctive prismatic cleavage at angles of approximately 90 degrees, making them easy to identify in rock samples.
3. Pyroxenes play a significant role in determining the physical properties of rocks, such as density and color, influencing their classification.
4. These minerals are commonly found in mafic and ultramafic rocks, like basalt and peridotite, which are rich in iron and magnesium.
5. The study of pyroxenes can provide insights into the conditions under which rocks form, including temperature, pressure, and the composition of the original magma.

Review Questions

• How does the structure of pyroxene influence its identification in rock samples?
  • The structure of pyroxene is characterized by a specific arrangement of silicate tetrahedra that leads to its distinct prismatic cleavage at angles close to 90 degrees. This unique cleavage pattern helps geologists identify pyroxenes during rock analysis. Additionally, the mineral's crystal habit and color variations further assist in distinguishing it from other silicate minerals found in igneous and metamorphic rocks.
• Discuss the role of pyroxene in understanding the composition and formation of igneous rocks.
  • Pyroxene is a key mineral in igneous rocks, where it significantly influences their composition and characteristics. By analyzing the presence and abundance of pyroxene within these rocks, geologists can infer details about the original magma's temperature, pressure conditions, and chemical composition during solidification. The identification of different types of pyroxene also aids in classifying igneous rocks into mafic or ultramafic categories based on their mineral content.
• Evaluate how the study of pyroxene contributes to our understanding of Earth's mantle composition and geological processes.
  • The study of pyroxene is crucial for evaluating Earth's mantle composition since these minerals are abundant in both the upper mantle and various mantle-derived rocks. By examining their chemical variations and stability under different temperature and pressure conditions, scientists can gain insights into mantle dynamics and magma formation processes. This information helps create models of Earth's internal processes, including plate tectonics and volcanic activity, enhancing our understanding of geological phenomena on a global scale.

Related terms

Silicate minerals:

A large group of minerals that contain silicon and oxygen, making up about 90% of the Earth's crust.

Igneous rocks: Rocks formed through the cooling and solidification of magma or lava, which often contain pyroxene as a primary mineral.

Cleavage:

The tendency of a mineral to break along flat, even surfaces, which is a key identifying feature in pyroxenes.