Felsic

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Felsic

Felsic is a term used in geology

Geology

Geology is the science and study of the solid and liquid matter that constitute the Earth. The field of geology encompasses the study of the composition, structural geology, physical properties, dynamics, and History of the Earth of Earth materials, and the processes by which they are formed, moved, and changed....
to refer to silicate minerals

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
, magma

Magma

Magma is molten Rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles....
, and rocks

Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
which are enriched in the lighter elements such as silicon

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
, oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
, aluminium

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
, sodium

Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
, and potassium

Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
. The term combines the words "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....
" and "silica." Felsic minerals are usually light in color and have specific gravities

Specific gravity

Specific gravity is defined as the ratio of the density of a given solid or liquid substance to the density of water at a specific temperature and pressure, typically at 4?C and , making it a dimensionless quantity ....
less than 3. Common felsic minerals include 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?....
, muscovite

Muscovite

Muscovite is a Silicate minerals mineral of aluminium and potassium with formula potassiumaluminum22, or 236....
, orthoclase

Orthoclase

Orthoclase is an important Silicate minerals mineral which forms igneous rocks. The name is from the Greek language for "straight fracture," because its two cleavage planes are at right angles to each other....
, and the sodium-rich 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 ....
feldspar

Feldspar

Granite

Granite is a common and widely occurring type of Intrusion , felsic, igneous rock rock . Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as Porphyry ....
. On the opposite side of the rock spectrum are the iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
and magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....
-rich 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"....
and ultramafic minerals and rocks.

In modern usage, the term acid rock, although sometimes used as a synonym, refers to a high silica content (greater than 63% SiO₂ by weight) 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....
such as rhyolite

Rhyolite

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Encyclopedia

Felsic is a term used in geology

Geology

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
, magma

Magma

Rock (geology)

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
, oxygen

Oxygen

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
, sodium

Sodium

Potassium

Feldspar

Specific gravity

Quartz

Muscovite

Muscovite is a Silicate minerals mineral of aluminium and potassium with formula potassiumaluminum22, or 236....
, orthoclase

Orthoclase

Plagioclase

Feldspar

Granite

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
and magnesium

Magnesium

Mafic

Volcanic rock

Volcanic rock is an igneous rock of Volcano origin.Texture Volcanic rocks are usually fine-grained or aphanitic to glassy in texture....
such as rhyolite

Rhyolite

This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous rock, volcanic rock , of felsic composition ....
. The term was used more broadly in older geologic literature. It is considered archaic as the terms acidic and basic rock were based on an incorrect idea dating from the 1800s that silicic acid

Silicic acid

Silicic acid is a general name for a family of chemical compounds of the element silicon, hydrogen, and oxygen, with the general formula [SiOx4-2x]n....
was the chief form of silicon occurring in rocks.

The term felsic is related to but not derived from the German adjective felsig ("rocky").

Classification of felsic rocks

In order for a rock to be classified as felsic it generally needs to contain >75% felsic minerals; namely quartz, orthoclase and plagioclase. Rocks with greater than 90% felsic minerals can also be called leucocratic, meaning 'light-coloured'.

Felsite

Felsite

Felsite is a very fine grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light colored rock that typically requires petrographic examination or chemical analysis for more precise definition....
is a petrologic

Petrology

In geology, petrology is the study of Rock s, and the conditions in which they form. Lithology once was approximately synonymous with petrography, but in current usage, lithology is a subdivision of petrology focusing on macroscopic hand-sample or outcrop-scale description of rocks, while petrography is the speciality that deals with m...
field term used to refer to very fine grained or aphanitic, light colored volcanic rocks that may be later reclassified after a more detailed microscopic or chemical analysis.

In some cases, felsic volcanic rocks may contain phenocryst

Phenocryst

A phenocryst is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock Matrix of a porphyritic igneous rock....
s of 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"....
minerals, usually hornblende

Hornblende

Hornblende is a complex silicate minerals series of minerals. Hornblende is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole....
, pyroxene

Pyroxene

The pyroxenes are a group of important rock-forming silicate minerals found in many igneous and metamorphic rock rock . They share a common structure comprised of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems....
or a feldspar mineral, and may need to be named after their phenocryst mineral, such as 'hornblende-bearing felsite'.

The chemical name of a felsic rock is given according to 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....
of Le Maitre (1975). However, this only applies to volcanic rocks. If the rock is analyzed and found to be felsic but is metamorphic

Metamorphic rock

Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form"....
and has no definite volcanic protolith

Protolith

Protolith refers to the precursor lithology of a metamorphic rock.For example, the protolith of a slate is a shale or mudstone. Metamorphic rocks can be derived from any other rock and thus have a wide variety of protoliths....
it may be sufficient to simply call it a 'felsic schist'. There are examples known of highly sheared granites which can be mistaken for rhyolites.

For phaneritic felsic rocks, the QAPF diagram

QAPF diagram

A QAPF diagram is a double triangle diagram which is used to classify igneous rocks based on mineralogy composition. The acronym, QAPF, stands for "Quartz, feldspar, Plagioclase, Feldspathoid "....
should be used, and a name given according to the granite

Granite

Granite is a common and widely occurring type of Intrusion , felsic, igneous rock rock . Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as Porphyry ....
nomenclature. Often the species of mafic minerals is included in the name, for instance hornblende-bearing granite, pyroxene

Pyroxene

Tonalite

Tonalite is an igneous rock, plutonic rock , of felsic composition, with phaneritic texture. Feldspar is present as plagioclase with 10% or less alkali feldspar....
or augite

Augite

Augite is a Silicate_minerals#Single_chain_inosilicates: mineral described chemically as SiO3 or calcium magnesium iron silicate. The crystals are monoclinic and prismatic....
megacrystic monzonite

Monzonite

Monzonite is an intermediate igneous intrusive rock composed of approximately equal amounts of sodic to intermediate plagioclase and orthoclase feldspars with minor amounts of hornblende, biotite and other minerals....
as the term granite already assumes feldspar and quartz.

The rock texture thus determines the basic name of a felsic rock.

Rock Texture	Name of Felsic Rock
Pegmatitic	Granite Granite Granite is a common and widely occurring type of Intrusion , felsic, igneous rock rock . Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as Porphyry .... pegmatite Pegmatite Pegmatite is a very coarse-grained igneous rock that has a grain size of 20 mm or more; such rocks are referred to as pegmatitic.Most pegmatites are composed of quartz, feldspar and mica; in essence a "granite"....
Coarse grained (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 .... )	Granite Granite Granite is a common and widely occurring type of Intrusion , felsic, igneous rock rock . Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as Porphyry ....
Coarse grained and porphyritic	Porphyritic granite Granite Granite is a common and widely occurring type of Intrusion , felsic, igneous rock rock . Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as Porphyry ....
Fine grained (aphanitic)	Rhyolite Rhyolite This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous rock, volcanic rock , of felsic composition ....
Fine grained and porphyritic	Porphyritic rhyolite Rhyolite This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous rock, volcanic rock , of felsic composition ....
Pyroclastic	Rhyolitic tuff Tuff Tuff is a type of Rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is also sometimes called tufa, particularly when used as construction material.... or breccia Breccia Breccia is a rock composed of angular fragments of several minerals or rocks in a Matrix , that is a Cementation material, that may be similar or different in composition to the fragments....
Vesicular Vesicular texture Vesicular texture is a volcanic Rock texture characterised by, or containing, many vesicles. The texture is often found in extrusive aphanite, or glassy, igneous rock....	Pumice Pumice File:Pumice stone444.jpgFile:Pumice stone detail444.jpgPumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano....
Amygdaloidal	None
Vitreous (Glassy) Vitreous Vitreous or glassy refers to a material in an amorphous state , thereby forming a glass. In such a state, the constituent atoms do not exhibit the long-range order that is characteristic of crystals....	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.... or porcellanite

Felsic

Classification of felsic rocks

See also