Olivine

Definition

Olivine is a common mineral found in the Earth's mantle and is primarily composed of magnesium and iron silicate. It plays a crucial role in understanding magma composition, generation processes, and the relationship between tectonics and magma. As a major component of ultramafic rocks, olivine can influence the properties of magma and provide insights into the conditions under which it forms.

5 Must Know Facts For Your Next Test

1. Olivine is one of the first minerals to crystallize from magma during the cooling process, making it significant for understanding magma evolution.
2. The presence of olivine in basaltic lava can indicate the degree of partial melting that occurred in the mantle.
3. Olivine is usually green in color, which can help identify it in hand samples or thin sections of rocks.
4. Variations in olivine composition can affect the viscosity of magma, influencing volcanic activity and eruption styles.
5. In tectonic settings, olivine-rich peridotites can be found at mid-ocean ridges and subduction zones, helping geologists understand mantle dynamics.

Review Questions

• How does olivine's crystallization impact the evolution of magma?
  • Olivine crystallizes early during the cooling of magma, which means it plays a key role in determining the mineralogy and composition of the resulting rock. As olivine forms, it removes magnesium and iron from the liquid phase, affecting the overall chemistry of the remaining melt. This process influences the types of minerals that will crystallize later and shapes the characteristics of volcanic rocks such as basalt.
• Discuss how olivine contributes to our understanding of tectonic processes at mid-ocean ridges.
  • At mid-ocean ridges, olivine-rich peridotite from the mantle is partially melted to form basaltic magma. The presence of olivine helps researchers understand the processes of melt generation and migration within the mantle. By studying olivine in this context, scientists can gain insights into mantle convection and how tectonic activity leads to volcanic eruptions and seafloor spreading.
• Evaluate the significance of olivine composition variations on volcanic activity and eruption styles in different tectonic settings.
  • Variations in olivine composition can significantly impact magma viscosity, which in turn affects eruption styles across different tectonic settings. In subduction zones, for example, olivine-rich magmas may lead to explosive eruptions due to increased viscosity and gas retention. Conversely, lower viscosity magmas enriched with olivine at mid-ocean ridges typically result in more effusive eruptions. Analyzing these variations allows researchers to predict volcanic behavior and assess potential hazards.

Related terms

Peridotite: A dense, coarse-grained igneous rock that consists mostly of olivine and is often found in the Earth's mantle.

Basalt:

A common volcanic rock that is typically rich in iron and magnesium, often containing olivine as one of its primary minerals.

Mantle:

The thick layer of the Earth located between the crust and the core, where olivine is a dominant mineral component.