Igneous rocks come in four basic varieties; ultramafic, mafic, intermediate, and felsic. These rocks are each composed of different suites of minerals and are derived from magmas which have different properties. Each of these magma types (and their rocks) are typically produced in specific locations on the earth and each magma type is generated by a specific set of tectonic processes.
The minerals found in the rocks of each magma type can be related to Bowen's Reaction Series. BRS shows the relationship among the 8 rock forming minerals (see below). For example, minerals at the top of the series tend to be iron and magnesium rich, low in silica, very hot, and produce dark colored minerals, such a Pyroxene, Amphibole, and Ca Plagioclase. Minerals at the bottom of BRS tend to be rich in sodium and potassium, high in silica, cooler in temperature, and produce light colored minerals, such as Na Plagioclase, Orthoclase, and Quartz.
Contributed by Lynn Fichter