Mineralogical Classification of Intrusive Igneous Rocks
Intrusive igneous rocks crystallize at some depth within the Earth's crust and thus are completely crystalline, generally unlayered and consist of interlocking crystals that are medium to coarse grained. Differing proportions of light and dark minerals result in a colour range from light to dark. These colour variations, the presence or absence of quartz, and the type of dark coloured mineral, are used to distinguish the different kinds of intrusive rocks.
|To use this figure, read from the bottom up. You can decide what the rock is from the mineral it contains. For example, if the rock is dark coloured and consists mainly of pyroxene and olivine, with about 20% plagioclase, it is a gabbro; if it has 25% combined mica and amphibole, 20% quartz, 10% orthoclase and the rest is plagioclase, it is a granodiorite. Links are provided in the diagram to descriptions of each of the minerals and rock types.|