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Igneous rock (igneous from Latin igneus 'fiery'), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust.
British Geological Survey rock classification scheme; Igneous rock classification Archived 2005-08-29 at the Wayback Machine; Rock Types Article by Encyclopædia Britannica; Classification of common rocks and soils; Metamorphic Rock Classification; Volcanic rocks; Earth Science Education Unit virtual rock kit
QAPF diagram for classification of plutonic rocks. A QAPF diagram is a doubled-triangle plot diagram used to classify intrusive igneous rocks based on their mineralogy.The acronym QAPF stands for "Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid)", which are the four mineral groups used for classification in a QAPF diagram.
In this top of a QAPF diagram for classification of plutonic rocks, silicic rocks are uncoloured at the top of the figure (Q is for Quartz which is pure silica) Silicic is an adjective to describe magma or igneous rock rich in silica. The amount of silica that constitutes a silicic rock is usually defined as at least 63 percent. [1]
The TAS classification should be applied only to rocks for which the mineral mode analysis cannot be determined. Otherwise, a scheme based on mineralogy, such as the QAPF diagram, or one of the other diagrams available for igneous rocks may be suitable. Before classifying rocks using the TAS diagram, the chemical analyses must be recalculated ...
Igneous textures are used by geologists in determining the mode of origin of igneous rocks and are used in rock classification. The six main types of textures are phaneritic , aphanitic , porphyritic , glassy , pyroclastic , and pegmatitic .
Metamorphic rocks are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism, meaning to "change in form". The result is a profound change in physical properties ...
They are classified under the IUGS Nomenclature for Igneous Rocks (Le Maitre et al., 1989) separately; this is primarily because they are rare, have peculiar mineralogy and do not fit classical classification schemes. For example, the TAS scheme is inappropriate due to the control of mineralogy by potassium, not by calcium or sodium.