Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silica, oxygen, aluminium, sodium, and potassium. The term combines the words "feldspar" and "silica." Felsic minerals are usually light in color and have specific gravities less than 3. Common felsic minerals include quartz, biotite, muscovite, hornblende, orthoclase, and the sodium rich plagioclase feldspars. The most common felsic rock is granite. On the opposite side of rock spectrum are the iron and magnesium rich mafic and ultramafic minerals and rocks. Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history and the processes that shape it. ... The silicate minerals make up the the largest and most important class of rock-forming minerals. ... Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ... Sedimentary, volcanic, plutonic, metamorphic rock types of North America. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless Atomic mass 15. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... Feldspar is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Quartz is amongst one of the most common minerals in the Earths continental crust. ... A Biotite slice Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. ... Muscovite layer Muscovite, also known as potash mica, is a phyllosilicate mineral of aluminium and potassium with formula: KAl2(AlSi3O10)(F,OH)2. ... Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ... Orthoclase (KAlSi3O8) is an important igneous rock forming tectosilicate mineral. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... Feldspar is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... Quarrying granite for the Mormon Temple, Utah Territory. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white Atomic mass 24. ... In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... Ultramafic (or ultrabasic) rocks are igneous rocks with very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). ...

The term acid rock, although sometimes used as a synonym, in current usage refers to a high silica content (greater than 63% SiO₂ by weight) volcanic rock such as rhyolite. 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 1800's that silicic acid was the chief form of silicon occurring in rocks. Ignimbrite is a deposit of a pyroclastic flow. ... Silicic acid is a general name for a family of chemical compounds of silicon, hydrogen, and oxygen, with the general formula [SiOx(OH)4-2x]n. ...

Classification of felsic rocks

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

Felsite' is a petrologic 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. Felsite is a very fine to cryptocrystalline igneous rock that may or may not contain larger crystals, called phenocrysts, that are typical of many porphyritic igneous rocks. ... Petrology is a field of geology which focuses on the study of rocks and the conditions by which they form. ... An aphanite is an igneous rock with a fine-grained structure. ... This article is about volcanoes in geology. ...

In some cases, felsic volcanic rocks may contain phenocrysts of mafic minerals, usually hornblende or biotite, or a feldspar mineral, and may need to be named after their phenocryst mineral, such as 'hornblende-bearing felsite'. Example of phenocrysts in rhomb porphyry from the Oslo rift area in Norway A phenocryst is a relatively large and usually conspicuous crystal formed in the mass of a porphyritic igneous rock. ... In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ... A Biotite slice Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. ...

The chemical name of a felsic rock is given according to the TAS diagram of Le Maitre (1975). However, this only applies to volcanic rocks. If the rock is analyzed and found to be felsic but is metamorphic and has no definite volcanic protolith 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. The term Metamorphic can be associated with a number of meanings:- Metamorphic rock The term for rocks that have been transformed by extreme heat and pressure. ... Protolith refers to the precursor rock of a given lithology. ... Study of geological shear is related to the study of structural geology, rock microstructure or rock texture and fault mechanics. ...

For phaneritic felsic rocks, the QAPF diagram should be used, and a name given according to the granite nomenclature. Often the species of mafic minerals is included in the name, for instance hornblende-bearing granite, pyroxene tonalite or augite megacrystic monzonite as the term granite already assumes feldspar and quartz. A QAPF diagram is a double triangle diagram which is used to classify igneous rocks based on mineralogic composition. ... Quarrying granite for the Mormon Temple, Utah Territory. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic texture. ... Augite is a mafic mineral described chemically as (Ca, Na)(Mg, Fe, Al)(Al, Si)2O6 or calcium sodium magnesium iron aluminium silicate. ... Monzonite is a felsic to 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. ...

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

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. ... Quarrying granite for the Mormon Temple, Utah Territory. ... 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. ... Phaneritic is a term usually used to refer to igneous rock grain size. ... Quarrying granite for the Mormon Temple, Utah Territory. ... (For other meanings of Porphyr, see Porphyry) The baptismal font in the Cathedral of Magdeburg is made of rose porphyry from a site near Assuan, Egypt Porphyry is a very hard red, green or purple igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a... Quarrying granite for the Mormon Temple, Utah Territory. ... An aphanite is an igneous rock with a fine-grained structure. ... Rhyolite Rhyolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... Rhyolite Rhyolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... Pyroclastic rocks are formed from lavas which are ejected into the air, as occur in pyroclastic flows or Plinian eruptions. ... Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo and pronounced tuf) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ... Breccia, derived from the Latin word for broken, is a sedimentary rock composed of angular fragments in a matrix that may be of a similar or a different material. ... Vesicular texture is a volcanic rock texture characterised by, or containing, many vesicles. ... Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... Amygdaloid, derived from the Latin for almond, can refer to: the amygdala in the brain. ... Obsidian from Lake County, Oregon Top stone is obsidian, below that is pumice and in lower right hand is rhyolite (light color) Obsidian is a type of naturally occurring glass, produced by volcanoes (igneous origin) when a felsic lava cools rapidly and freezes without sufficient time for crystal growth (see...

Reference

• Le Maitre, L.E., ed. 2002. Igneous Rocks: A Classification and Glossary of Terms 2nd edition, Cambridge.

See also

• QAPF diagram
• List of minerals
• List of rocks
• Granite
• Mafic