Such texture forms in volcanoes, along fault zones, and in landslides. Igneous rock chemistry is determined mainly by the source of the magma and any interactions between magma and the rocks through which it migrates. Chemical composition usually is indicated by the minerals or color of an igneous rock. Rich in feldspars and silica. Typical of continental crust.
Plagioclase feldspars make up more than two-thirds of total feldspars.
Found in association with subduction zones. Rich in magnesium and iron with less silica. Typical of oceanic crust. Derived from the mantle. Igneous rock classification Texture combined with chemical composition is the basis for modern classification of igneous rocks.