Granite

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

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

- Granite

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Mica

That individual mica crystals can easily be split into extremely thin elastic plates.

Sheets of mica
Photomicrographs of a thin section containing phlogopite. In cross-polarized light on left, plane-polarized light on right.
Dark mica from eastern Ontario
Mica flakes embedded in a fresco for glitter
Muscovite windows
Silver mica capacitors
Micanite or mica for isolated mounting of transistors (top, right) and mica discs.
Hand carved from mica from the Hopewell tradition
Kirazuri printing technique adds mica powder to the gelatin solution as adhesive, here printed on the background.
View of tetrahedral sheet structure of mica. The apical oxygen ions are tinted pink.
View of trioctahedral sheet structure of mica. The binding sites for apical oxygen are shown as white spheres.
View of trioctahedral sheet structure of mica emphasizing octahedral sites
View of dioctahedral sheet structure of mica. The binding sites for apical oxygen are shown as white spheres.
View of dioctahedral sheet structure of mica emphasizing octahedral sites
View of trioctahedral mica structure looking at surface of a single layer
View of trioctahedral mica structure looking along sheets

It is particularly prominent in many granites, pegmatites, and schists, and "books" (large individual crystals) of mica several feet across have been found in some pegmatites.

Granitoid

Generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar.

Granite rock hand sample
Illustration of continental collision as a result of convergence

The terms granite and granitic rock are often used interchangeably for granitoids; however, granite is just one particular type of granitoid.

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

in some special circumstances they host important mineral deposits (ores): for example, tungsten, tin, and uranium are commonly associated with granites and diorites, whereas ores of chromium and platinum are commonly associated with gabbros.

Feldspar

Feldspars are a group of rock-forming aluminium tectosilicate minerals, containing sodium, calcium, potassium, or barium.

Feldspar crystal (18×21×8.5 cm) from Jequitinhonha valley, Minas Gerais, southeastern Brazil
Compositional phase diagram of the different minerals that constitute the feldspar solid solution.
Diagram showing part of a crankshaft chain of feldspar
Feldspar crystal structure viewed along the c axis
Feldspar crystal structure viewed along the a axis
Feldspar crystal structure viewed along the b axis
Specimen of rare plumbian (lead-rich) feldspar
Perched on crystallized, white feldspar is an upright 4 cm aquamarine crystal
Feldspar and moonstone, from Sonora, Mexico
Schorl crystal on a cluster of euhedral feldspar crystals
First X-ray view of Martian soil—feldspar, pyroxenes, olivine revealed (Curiosity rover at "Rocknest", October 17, 2012).<ref name="NASA-20121030">{{cite web |last=Brown |first=Dwayne |title=NASA Rover's First Soil Studies Help Fingerprint Martian Minerals |url=http://www.nasa.gov/home/hqnews/2012/oct/HQ_12-383_Curiosity_CheMin.html |date=October 30, 2012 |publisher=NASA |access-date=October 31, 2012}}</ref>
Lunar ferrous anorthosite #60025 (plagioclase feldspar). Collected by Apollo 16 from the Lunar Highlands near Descartes Crater. This sample is currently on display at the National Museum of Natural History in Washington, D.C.

The perthitic textures in the alkali feldspars of many granites can be seen with the naked eye.

Hornblende

Complex inosilicate series of minerals.

Hornblende crystal (dark green) about 35 mm long, with apatite (white)
Hornblende diorite from the Henry Mountains, Utah, US

Hornblende is most often confused with the pyroxene series and biotite mica, which are also dark minerals found in granite and charnockite.

Porphyritic

Adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts.

Porphyritic texture in a granite. This is an intrusive porphyritic rock. The white, square feldspar phenocrysts are much larger than crystals in the surrounding matrix; eastern Sierra Nevada, Rock Creek Canyon, California.
A porphyritic volcanic sand grain, as seen under the petrographic microscope. The large grain in the middle is of a much different size class than the small needle-like crystals around it. Scale box in millimeters.
Andesite porphyry from summit of O'Leary Peak. This is an extrusive porphyritic rock, as the pink (and black) phenocrysts are clearly visible, in contrast to the grey groundmass with its microscopic crystals.

Porphyritic intrusive rocks have a matrix with individual crystals easily distinguished with the eye, but one group of crystals appearing clearly much bigger than the rest, as in a porphyritic granite.

Dike (geology)

Sheet of rock that is formed in a fracture of a pre-existing rock body.

A magmatic dike cross-cutting horizontal layers of sedimentary rock, in Makhtesh Ramon, Israel
A dike of lamprophyre near the Shiprock volcanic plug, New Mexico, that has resisted the erosion that removed some of the softer rock into which the dike was originally intruded
Simplified map of the en echelon dike set at Jagged Rock, Arizona, US. The total dike length is about 1.45 km.
A composite dike in Orkney, Scotland, with bostonite margins and a camptonite center
Mackenzie dike swarm
Sheeted dikes of the Lizard complex, Cornwall, England
Ring dike of the Questa caldera, New Mexico, US
Clastic dike (left of notebook) in the Chinle Formation in Canyonlands National Park, Utah

The range of compositions in a composite dike can go all the way from diabase to granite, as is observed in some dikes of Scotland and northern Ireland.

Porphyry (geology)

Textural term for an igneous rock consisting of coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass.

"Imperial Porphyry" from the Red Sea Mountains of Egypt
A waterworn cobble of porphyry
Rhyolite porphyry from Colorado; scale bar in lower left is 1 cm
The Tetrarchs, a porphyry sculpture sacked from the Byzantine Philadelphion palace in 1204, Treasury of St. Marks, Venice
Carmagnola, an imperial porphyry head in Venice thought to represent Justinian
Porphyry sarcophagus, Istanbul Archaeological Museum
Sarcophagus of Frederick II in Palermo Cathedral, Sicily, made of porphyry
Interior of the de' Medici Cappella dei Principi in Florence (1870s photograph)
Sarcophagus of Napoleon in Les Invalides, Paris, made of quartzite with a pedestal of green porphyry

Porphyries may be aphanites or phanerites, that is, the groundmass may have microscopic crystals as in basalt, or crystals easily distinguishable with the eye, as in granite.

Phenocryst

Early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock.

Granites often have large feldspathic phenocrysts. This granite, from the Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coin (diameter 2.3 cm) for scale.
Photomicrograph of a porphyritic-aphanitic felsic rock, from the Middle Eocene in the Blue Ridge Mountains of Virginia. Plagioclase phenocrysts (white) and hornblende phenocryst (dark; intergrown with plagioclase) are set in a fine matrix of plagioclase laths that show flow structure.

In rapakivi granites, phenocrysts of orthoclase are enveloped within rinds of sodic plagioclase such as oligoclase.

Syenite

Syenite
QAPF diagram that shows the quartz (Q), alkali feldspar (A), and plagioclase (P) composition of syenite
Leucocratic variety of nepheline syenite from Sweden (särnaite)
Boulders of syenite near Concord, North Carolina, c. 1910.

Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%).