(Mg,Fe)2SiO4

Definition

(Mg,Fe)2SiO4 represents a solid solution series between forsterite (Mg2SiO4) and fayalite (Fe2SiO4), which are both members of the olivine mineral group. This term reflects the variability in magnesium (Mg) and iron (Fe) content in the crystal structure, highlighting the importance of these elements in determining the mineral's physical properties and stability. Understanding this solid solution is crucial for identifying olivine in various geological settings and its role in the Earth's mantle.

5 Must Know Facts For Your Next Test

1. (Mg,Fe)2SiO4 can range in composition from completely magnesium-rich (forsterite) to entirely iron-rich (fayalite), influencing its color, density, and stability.
2. The presence of iron in (Mg,Fe)2SiO4 affects its optical properties, making fayalite darker than forsterite due to increased absorption of light.
3. Olivine is a significant mineral in the Earth's upper mantle, often forming under high-temperature and high-pressure conditions during magmatic processes.
4. The partitioning of Mg and Fe between olivine and other minerals is critical in petrology, particularly in understanding magmatic differentiation and metamorphic processes.
5. The stability of olivine at varying temperatures and pressures is an essential factor in geothermobarometry, helping to estimate the conditions of rock formation.

Review Questions

• How does the variability in Mg and Fe content within (Mg,Fe)2SiO4 influence its physical properties?
  • The variability in magnesium and iron content within (Mg,Fe)2SiO4 significantly affects its physical properties such as color, density, and melting point. For example, forsterite, being magnesium-rich, has a lighter color and higher melting point compared to fayalite, which is iron-rich and appears darker. This variation is crucial for mineral identification and provides insight into the geological processes that formed the rock.
• What role does (Mg,Fe)2SiO4 play in understanding magmatic differentiation processes?
  • (Mg,Fe)2SiO4 serves as a key indicator in magmatic differentiation processes because its composition reflects the conditions under which it crystallizes from a magma. As magma cools, olivine forms early due to its high melting point; its composition can reveal information about the source of the magma and subsequent crystallization sequences. This understanding helps geologists interpret the evolution of igneous rocks.
• Evaluate the significance of (Mg,Fe)2SiO4 in terms of its stability under varying temperature and pressure conditions in the Earth's mantle.
  • (Mg,Fe)2SiO4 is critically significant for understanding the stability of minerals within the Earth's mantle as it forms under specific temperature and pressure conditions. The stability of forsterite versus fayalite can indicate different thermal gradients and tectonic environments within the mantle. By studying how these compositions behave under varying conditions, researchers can gain insights into mantle convection patterns, rock formation processes, and even the history of volcanic activity on Earth.

Related terms

Forsterite: A magnesium-rich end member of the olivine group, characterized by its high melting point and occurrence in ultramafic rocks.

Fayalite: An iron-rich end member of the olivine group, typically found in igneous rocks and associated with lower temperature formation conditions.

Solid Solution: A mineralogical concept where two or more different chemical elements can substitute for one another within the same crystal structure without altering the overall structure.