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QAPF diagram

 
QAPF Diagram

 
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A QAPF diagram is a double triangle diagram
Diagram

A diagram is a 2D geometric model symbolic representation of information according to some visualization technique. Sometimes, the technique uses a Three-dimensional space visualization which is then graphical projection onto the 2D surface....
 which is used to classify igneous rock
Igneous rock

Igneous rock is one of the three main Rock types . Igneous rock is formed by magma being cooled and becoming solid . They may form with or without crystallization, either below the surface as Intrusion rocks or on the surface as extrusive rocks....
s based on mineralogic
Mineralogy

Mineralogy is an Earth Science focused around the chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization....
 composition. The acronym, QAPF, stands for "Quartz
Quartz

Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
, Alkali feldspar
Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's Crust .Feldspars crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock....
, Plagioclase
Plagioclase

Plagioclase is a very important series of Silicate minerals minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series ....
, Feldspathoid
Feldspathoid

The feldspathoids are a group of Silicate minerals minerals which resemble feldspars but have a different structure and much lower silica content....
 (Foid)". These are the mineral
Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
 groups used for classification in QAPF diagram. Q, A, P and F percentages are normalized (recalculated so that their sum is 100%).

QAPF diagrams are mostly used to classify plutonic rocks
Intrusion

In geology, an intrusion is a body of igneous rock that has crystallized from molten magma below the surface of the Earth. Bodies of magma that solidify underground before they reach the surface of the earth are called plutons, named for Pluto , the Roman mythology of the underworld....
 (phaneritic
Phaneritic

Phaneritic is a term usually used to refer to igneous rocks Particle size. It means that the size of grains in the Rock are large enough to be distinguished with the unaided eye as opposed to aphanitic ....
 rocks) (Figure 1), but are also used to classify volcanic rock
Volcanic rock

Volcanic rock is an igneous rock of Volcano origin.Texture Volcanic rocks are usually fine-grained or aphanitic to glassy in texture....
s (Figure 2) if modal mineralogical compositions have been determined.






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A QAPF diagram is a double triangle diagram
Diagram

A diagram is a 2D geometric model symbolic representation of information according to some visualization technique. Sometimes, the technique uses a Three-dimensional space visualization which is then graphical projection onto the 2D surface....
 which is used to classify igneous rock
Igneous rock

Igneous rock is one of the three main Rock types . Igneous rock is formed by magma being cooled and becoming solid . They may form with or without crystallization, either below the surface as Intrusion rocks or on the surface as extrusive rocks....
s based on mineralogic
Mineralogy

Mineralogy is an Earth Science focused around the chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization....
 composition. The acronym, QAPF, stands for "Quartz
Quartz

Quartz is the most abundant mineral in the Earth's continental crust . It is made up of a Crystal structure of silica tetrahedra. Quartz has a hardness of 7 on the Mohs scale and a density of 2.65 g/cm?....
, Alkali feldspar
Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's Crust .Feldspars crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock....
, Plagioclase
Plagioclase

Plagioclase is a very important series of Silicate minerals minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series ....
, Feldspathoid
Feldspathoid

The feldspathoids are a group of Silicate minerals minerals which resemble feldspars but have a different structure and much lower silica content....
 (Foid)". These are the mineral
Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
 groups used for classification in QAPF diagram. Q, A, P and F percentages are normalized (recalculated so that their sum is 100%).

QAPF diagrams are mostly used to classify plutonic rocks
Intrusion

In geology, an intrusion is a body of igneous rock that has crystallized from molten magma below the surface of the Earth. Bodies of magma that solidify underground before they reach the surface of the earth are called plutons, named for Pluto , the Roman mythology of the underworld....
 (phaneritic
Phaneritic

Phaneritic is a term usually used to refer to igneous rocks Particle size. It means that the size of grains in the Rock are large enough to be distinguished with the unaided eye as opposed to aphanitic ....
 rocks) (Figure 1), but are also used to classify volcanic rock
Volcanic rock

Volcanic rock is an igneous rock of Volcano origin.Texture Volcanic rocks are usually fine-grained or aphanitic to glassy in texture....
s (Figure 2) if modal mineralogical compositions have been determined. QAPF diagrams are not used to classify pyroclastic rock
Pyroclastic rock

Pyroclastic rocks or pyroclastics are clastic rocks composed solely or primarily of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed volcaniclastic....
s or volcanic rocks if modal mineralogical composition is not determined, instead the TAS classification
TAS classification

The TAS classification can be used to assign names to many common types of volcanic rocks based upon the relationships between the combined alkali content and the silica content....
 (Total-Alkali-Silica) is used. TAS is also used if volcanic rock contains volcanic glass (such as obsidian
Obsidian

Obsidian is a naturally occurring glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools without crystal growth....
). QAPF diagrams are also not used if mafic
Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric"....
 mineral
Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s make up more than 90% of the rock composition (for example: peridotite
Peridotite

A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic and ultrabasic, as the rock contains less than 45% silica....
s and pyroxenite
Pyroxenite

Pyroxenite is an ultramafic igneous Rock consisting essentially of minerals of the pyroxene group, such as augite and diopside, hypersthene, bronzite or enstatite....
s).

An exact name can be given only if the mineralogical composition is known, which cannot be determined in the field. Therefore, provisional or field classifications (Figures 3 and 4) are used, which are simplified versions of Figures 1 and 2.

QAPF diagrams were created by the International Union of Geological Sciences
International Union of Geological Sciences

The International Union of Geological Sciences is an international non-governmental organization devoted to international cooperation in the field of geology....
 (IUGS): Subcommission on the Systematics of Igneous Rocks. The diagrams are accepted by geologists worldwide as a classification of igneous, especially plutonic rocks.

Image:QAPF diagram plutonic.gif|Figure 1. This classification is used if rock sample has phaneritic texture (plutonic rocks). Image:QAPF diagram volcanic.gif|Figure 2. This classification is used if rock sample has fine-grained texture (volcanic rocks) but modal mineralogical composition can be determined. Image:QAPF diagram plutonic field.gif|Figure 3. This is provisional classification for phaneritic igneous rocks (field classification). Image:QAPF diagram volcanic field.gif|Figure 4. This is provisional classification for fine-grained igneous rocks (field classification).



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