Igneous Rock
One of the three basic types of rock that also include sedimentary and metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment.. Igneous rocks are formed by the solidification of magmaMolten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava. and comprised predominately of silicateThe most abundant group of minerals in Earth's crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the minerals. Based on bulk chemical analysis, igneous rocks can be grouped into four major groups based on their SiO2 content:
| 1. | FelsicOne of the two broad categories of silicate minerals, the other being mafic, based on the magnesium (Mg) and/or iron (Fe) content. Felsic indicates silicate minerals that are not predominantly comprised of Mg and/or Fe. The term is derived from feldspar + ic (having the character or form of). The: | SiO2 > 65% |
| 2. | Intermediate: | 55% < SiO2 < 65% |
| 3. | MaficOne of the two broad categories of silicate minerals, the other being felsic, based on its magnesium (Mg) and/or iron (Fe) content. Mafic indicates silicate minerals that are predominantly comprised of Mg and/or Fe.The term is derived from those major constituents: Magnesium + Ferrum (Latin for iron) + ic (having: | 45% < SiO2 < 55% |
| 4. | UltramaficTerm used for silicate minerals with cations predominantly Mg and/or Fe. Mafic minerals are dominated by plagioclase and pyroxene, and also contain smaller amounts of olivine.: | SiO2 < 45% |
