Pyroxene

Definition

Pyroxene refers to a group of important rock-forming silicate minerals characterized by their single chain structure of silicon-oxygen tetrahedra. These minerals are crucial in the classification of igneous and metamorphic rocks due to their common occurrence and significance in geological processes. Pyroxenes are typically found in basalt and gabbro, and their properties, such as cleavage angles and color variations, are key for identifying and classifying different types of rocks.

5 Must Know Facts For Your Next Test

1. Pyroxenes can be classified into two main groups: orthopyroxenes (monoclinic) and clinopyroxenes (orthorhombic), which differ in their crystal structures.
2. Common pyroxene minerals include augite and enstatite, each with unique physical properties that help identify them in rock samples.
3. The cleavage of pyroxenes is typically two directions at nearly 90 degrees, which is a key distinguishing feature when identifying these minerals.
4. Pyroxenes often contain varying amounts of iron, magnesium, aluminum, and calcium, which can affect their color and density.
5. In addition to igneous rocks, pyroxenes also play a role in metamorphic rocks, where they can form under high-temperature and high-pressure conditions.

Review Questions

• How do the structural characteristics of pyroxenes influence their classification within the silicate mineral group?
  • The structural characteristics of pyroxenes are defined by their single chain arrangement of silicon-oxygen tetrahedra. This unique structure allows them to form distinct crystal systems, specifically orthopyroxene and clinopyroxene. These differences in crystal symmetry and arrangement directly impact how these minerals are classified within the broader category of silicate minerals.
• Discuss the role of pyroxenes in igneous rock classification, including their significance in identifying rock types.
  • Pyroxenes play a vital role in the classification of igneous rocks due to their widespread presence in volcanic and plutonic environments. The specific type of pyroxene present can provide critical information about the rock's formation conditions. For example, basalt typically contains clinopyroxene, while gabbro features orthopyroxene. Identifying these minerals helps geologists determine the chemical composition and cooling history of the rock.
• Evaluate the environmental conditions under which pyroxenes form and their implications for understanding geological processes.
  • Pyroxenes typically form under high-temperature conditions during the crystallization of magma or as a result of metamorphic processes involving intense heat and pressure. Their presence can indicate specific environmental conditions, such as those found in subduction zones or mid-ocean ridges. By studying pyroxenes and their formation conditions, geologists can gain insights into tectonic activity, magma evolution, and the thermal history of the Earth's crust.

Related terms

Silicate Minerals: A group of minerals that contain silicon and oxygen as their fundamental building blocks, making up the largest family of minerals in the Earth's crust.

Feldspar: A group of rock-forming minerals that are crucial for the composition of igneous and metamorphic rocks, often found alongside pyroxenes.

Mafic: Refers to igneous rocks that are rich in magnesium and iron, where pyroxenes are commonly present, influencing the rock's properties.