SiO2-FeO System Phase Diagram
The SiO2-FeO system is a binary solid solution system composed of silica (SiO2) and ferrous oxide (FeO). It is also known as the Iron Silicate System and is used to simulate the formation and behavior of iron-oxide-rich rocks. This system is important for understanding the evolution of iron and silica-rich magmas and their resulting rocks and minerals. The SiO2-FeO system phase diagram can be used to identify the mineral assemblage of an igneous rock and predict its evolution with temperature, pressure and other processes.
The SiO2-FeO system has four end-member components which are silica, iron (II) oxide, iron (III) oxide, and iron- and silica-rich intermediates. The assemblage of these four components depends on their relative concentrations, temperature, and pressure. At low concentrations, the end-member components appear in different proportions, giving various igneous rocks and minerals. The phase diagram of the system, which plots the relative concentrations of each component against temperature and pressure, provides a framework for understanding their relations and predicting the resulting minerals generated.
At low temperatures, silica and ferrous oxide are not significantly affected by pressure, so the system has two fields of vision. On the left side of the phase diagram, a near-pure SiO2 field occurs, containing quartz, felsic and mafic glass, and cristobalite. On the right side, a near-pure FeO field occurs, containing magnetite, maghemite, and hematite. Between these two extreme fields, the SiO2-FeO system can produce intermediate compositions, such as that of iron-rich andesite, dolerite, and basalt.
When pressure and temperature increase, the SiO2- FeO system produces an array of minerals, including pyroxenes and amphiboles, rather than just the end-member components. As the system reaches equilibrium, these minerals may combine to form intermediate-to-advanced stage rocks, such as tuffs, gabbros, and peridotites. For example, the phase diagram might indicate the presence of diopside and hornblende in an intermediate-level rock, which suggests the formation of diorite and granite.
The phases in the SiO2-FeO system are not only important for understanding rock formation but can also be used for ore formation. For example, at high temperatures and pressures, the system is capable of forming iron-oxide magnetite and hematite, which are important ore-forming minerals. Pressure dissolves the iron— forming molten iron-sulfide and iron-oxide veins in the host rock— which are good candidates for exploration and extraction.
Overall, the SiO2-FeO system is an essential tool for the study of the formation and evolution of igneous rocks, and can be used to infer the conditions under which magmas evolve and form rocks. Its phase diagrams are useful in determining the amounts of each component and can be used to identify the rock types produced at various temperatures and pressures. In addition, they can be used to study ore formation, helping assess the economic viability of a given site. Understanding this binary system can provide valuable insights into the formation of rocks and minerals, and the economic value of ore deposits.
