Felsic

A felsic volcanic lithic fragment, as seen in a petrographic microscope. Scale box is in millimeters.
Close-up of granite from Yosemite National Park.
A specimen of rhyolite.

Modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.

- Felsic

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Albite

Plagioclase feldspar mineral.

Albite from Crete
Albite

It is a common constituent in felsic rocks.

Orthoclase

Important tectosilicate mineral which forms igneous rock.

Adularia (KAlSi3O8) with pyrite (FeS2) incrustations

Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite.

Mafic

Silicate mineral or igneous rock rich in magnesium and iron.

Basalt

In contrast, the felsic rocks are typically light in color and enriched in aluminium and silicon along with potassium and sodium.

Igneous rock

One of the three main rock types, the others being sedimentary and metamorphic.

Volcanic eruptions of lava are major sources of igneous rocks. (Mayon volcano in the Philippines, erupting in 2009)
Natural columns of igneous rock separated from each other by columnar joints, in Madeira
Formation of igneous rock
Basic types of intrusions:
Extrusive igneous rock is made from lava released by volcanoes
Sample of basalt (an extrusive igneous rock), found in Massachusetts
Close-up of granite (an intrusive igneous rock) exposed in Chennai, India
Gabbro specimen showing phaneritic texture, from Rock Creek Canyon, eastern Sierra Nevada, California
Basic classification scheme for igneous rocks based on their mineral composition. If the approximate volume fractions of minerals in the rock are known, the rock name and silica content can be read off the diagram. This is not an exact method, because the classification of igneous rocks also depends on other components, yet in most cases it is a good first guess.
Total alkali versus silica classification scheme (TAS) as proposed in Le Maitre's 2002 Igneous Rocks – A classification and glossary of terms Blue area is roughly where alkaline rocks plot; yellow area is where subalkaline rocks plot.
AFM ternary diagram showing the relative proportions of Na2O + K2O (A for Alkali earth metals), FeO + Fe2O3 (F), and MgO (M) with arrows showing the path of chemical variation in tholeiitic and calc-alkaline series magmas
Schematic diagrams showing the principles behind fractional crystallisation in a magma. While cooling, the magma evolves in composition because different minerals crystallize from the melt. 1: olivine crystallizes; 2: olivine and pyroxene crystallize; 3: pyroxene and plagioclase crystallize; 4: plagioclase crystallizes. At the bottom of the magma reservoir, a cumulate rock forms.
Kanaga volcano in the Aleutian Islands with a 1906 lava flow in the foreground
A "skylight" hole, about {{cvt|6|m}} across, in a solidified lava crust reveals molten lava below (flowing towards the top right) in an eruption of Kīlauea in Hawaii
Devils Tower, an eroded laccolith in the Black Hills of Wyoming
A cascade of molten lava flowing into Aloi Crater during the 1969-1971 Mauna Ulu eruption of Kilauea volcano
Columnar jointing in the Alcantara Gorge, Sicily
A laccolith of granite (light-coloured) that was intruded into older sedimentary rocks (dark-coloured) at Cuernos del Paine, Torres del Paine National Park, Chile
An igneous intrusion cut by a pegmatite dike, which in turn is cut by a dolerite dike

Felsic magma, such as rhyolite, is usually erupted at low temperature and is up to 10,000 times as viscous as basalt.

Tonalite

A piece of tonalite on red granite gneiss from Tjörn, Sweden
QAPF diagram with tonalite field highlighted

Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic (coarse-grained) texture.

Volcanic rock

Rock formed from lava erupted from a volcano.

Ignimbrite, a volcanic rock deposited by pyroclastic flows
Photomicrograph of a volcanic lithic fragment (sand grain); upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter.
An aphanitic volcanic sand grain, with fine-grained groundmass, as seen under a petrographic microscope
Vesicular olivine basalt from La Palma (green phenocrysts are olivine).
A 15 cm piece of pumice supported by a rolled U.S. $20 bill demonstrates its very low density.
Aā next to pāhoehoe lava at the Craters of the Moon National Monument and Preserve, Idaho, United States.
A German example of latite, a type of volcanic rock
A sample of rhyolite
Basaltic scoria from Amsterdam Island in the Indian Ocean
Volcanic rocks, Porto Moniz, Madeira

They are often felsic (high in silica).

Quartz

Hard, crystalline mineral composed of silica .

Quartz crystal cluster from Tibet
Quartz crystal demonstrating transparency
A synthetic quartz crystal grown by the hydrothermal method, about 19 cm long and weighing about 127 grams
Granite rock in the cliff of Gros la Tête on Aride Island, Seychelles. The thin (1–3 cm wide) brighter layers are quartz veins, formed during the late stages of crystallization of granitic magmas. They are sometimes called "hydrothermal veins".
Crystal structure of α-quartz (red balls are oxygen, grey are silicon)
β-quartz
Herkimer diamond
Rock crystal
Ametrine
Amethyst
Blue quartz
Chalcedony
Citrine
Rose quartz
Prasiolite
Rutilated quartz
Sceptred quartz
Smoky quartz
Rock crystal jug with cut festoon decoration by Milan workshop from the second half of the 16th century, National Museum in Warsaw. The city of Milan, apart from Prague and Florence, was the main Renaissance centre for crystal cutting.<ref>{{cite book |title=The International Antiques Yearbook |year=1972 |page=78 |publisher=Studio Vista Limited |url=https://books.google.com/books?id=BVcvAQAAIAAJ|quote=Apart from Prague and Florence, the main Renaissance centre for crystal cutting was Milan.}}</ref>
Synthetic quartz crystals produced in the autoclave shown in Western Electric's pilot hydrothermal quartz plant in 1959
Fatimid ewer in carved rock crystal (clear quartz) with gold lid, c. 1000.

Quartz is a defining constituent of granite and other felsic igneous rocks.

Granite

Coarse-grained intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase.

Granite containing potassium feldspar, plagioclase feldspar, quartz, and biotite and/or amphibole
Thin section of granite
QAPF diagram with granite field highlighted in yellow
Mineral assemblage of igneous rocks
The Cheesewring, a granite tor in England
A granite peak at Huangshan, China
Pink granite at Hiltaba, South Australia (part of the Hiltaba Suite)
Granite with quartz veins at Gros la Tête cliff, Aride Island, Seychelles
Grus sand and granitoid it derived from
Granite dimension stone quarry in Taivassalo, Finland
Cleopatra's Needle, London
Granites (cut and polished surfaces)
The granite castle of Aulanko in Hämeenlinna, Finland
Curling stones
Granite was used for setts on the St. Louis riverfront and for the piers of the Eads Bridge (background)
The granite peaks of the Cordillera Paine in the Chilean Patagonia
alt=Half Dome, Yosemeite National Park|Half Dome, Yosemite National Park, is actually a granite arête and is a popular rock climbing destination
Rixö red granite quarry in Lysekil, Sweden
Granite in Auyuittuq National Park on Baffin Island, Canada
Granite in Paarl, South Africa

Granite forms from silica-rich (felsic) magmas.

Felsite

Very fine-grained volcanic rock that may or may not contain larger crystals.

Felsite covered with dendritic pyrolusite formations.
Dike of felsite on Islay in Scotland

The mass of the rock consists of a fine-grained matrix of felsic materials, particularly quartz, sodium and potassium feldspar, and may be termed a quartz felsite or quartz porphyry if the quartz phenocrysts are present.

Volcano

Rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

Bromo volcano in Indonesia. This country has more than 130 active volcanoes, one of which is a supervolcano, making Indonesia the country with the most active volcanoes in the world.
Cordillera de Apaneca volcanic range in El Salvador. The country is home to 170 volcanoes, 23 which are active, including two calderas, one being a supervolcano. El Salvador has earned the epithets endearment La Tierra de Soberbios Volcanes, (The Land of Magnificent Volcanoes).
Sabancaya volcano erupting, Peru in 2017
Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station, May 2006
An eruption of Mount Pinatubo on June 12, 1991, three days before its climactic eruption
Fountain of lava erupting from a volcanic cone in Hawaii, 1983
Aerial view of the Barren Island, Andaman Islands, India, during an eruption in 1995. It is the only active volcano in South Asia.
Map showing the divergent plate boundaries (oceanic spreading ridges) and recent sub-aerial volcanoes (mostly at convergent boundaries)
Lakagigar fissure vent in Iceland, the source of the major world climate alteration of 1783–84, has a chain of volcanic cones along its length.
Skjaldbreiður, a shield volcano whose name means "broad shield"
Izalco volcano, the youngest volcano in El Salvador. Izalco erupted almost continuously from 1770 (when it formed) to 1958, earning it the nickname of "Lighthouse of the Pacific".
Cross-section through a stratovolcano (vertical scale is exaggerated):
Satellite images of the 15 January 2022 eruption of Hunga Tonga-Hunga Haʻapai
Pāhoehoe lava flow on Hawaii. The picture shows overflows of a main lava channel.
The Stromboli stratovolcano off the coast of Sicily has erupted continuously for thousands of years, giving rise to its nickname "Lighthouse of the Mediterranean"
Columnar-jointed basalt lava erupted from a volcano, South Penghu Marine National Park in Taiwan
Light-microscope image of tuff as seen in thin section (long dimension is several mm): The curved shapes of altered glass shards (ash fragments) are well preserved, although the glass is partly altered. The shapes were formed around bubbles of expanding, water-rich gas.
Fresco with Mount Vesuvius behind Bacchus and Agathodaemon, as seen in Pompeii's House of the Centenary
Narcondam Island, India, is classified as a dormant volcano by the Geological Survey of India
Fourpeaked volcano, Alaska, in September 2006 after being thought extinct for over 10,000 years
Mount Rinjani eruption in 1994, in Lombok, Indonesia
Shiprock in New Mexico, US
Capulin Volcano National Monument in New Mexico, US
Koryaksky volcano towering over Petropavlovsk-Kamchatsky on Kamchatka Peninsula, Far Eastern Russia
Schematic of volcano injection of aerosols and gases
Solar radiation graph 1958–2008, showing how the radiation is reduced after major volcanic eruptions
Sulfur dioxide concentration over the Sierra Negra Volcano, Galapagos Islands, during an eruption in October 2005
Comparison of major United States supereruptions (VEI 7 and 8) with major historical volcanic eruptions in the 19th and 20th century. From left to right: Yellowstone 2.1 Ma, Yellowstone 1.3 Ma, Long Valley 6.26 Ma, Yellowstone 0.64 Ma . 19th century eruptions: Tambora 1815, Krakatoa 1883. 20th century eruptions: Novarupta 1912, St. Helens 1980, Pinatubo 1991.
The Tvashtar volcano erupts a plume 330 km (205 mi) above the surface of Jupiter's moon Io.
Olympus Mons (Latin, "Mount Olympus"), located on the planet Mars, is the tallest known mountain in the Solar System.

If the erupted magma contains a high percentage (>63%) of silica, the lava is described as felsic. Felsic lavas (dacites or rhyolites) are highly viscous and are erupted as domes or short, stubby flows. Lassen Peak in California is an example of a volcano formed from felsic lava and is actually a large lava dome.