What are intermediate rocks examples?
Granodiorite, diorite, syenite, phonolite
What does felsic mean?
Felsic rocks contain more than 65% silica
What minerals are enriched in felsic rocks?
Sodium and potassium
What minerals are depleted in felsic rocks?
Iron, magnesium, calcium
What are important minerals in felsic rocks?
Quartz, feldspathoid, soda feldspar, potash feldspar, muscovite
What color are felsic rocks typically?
Light-coloured
What are the most common felsic rocks?
Granite and rhyolite
What is a granitoid rock?
A common term for a group of plutonic rocks including granites
What does rhyolite resemble?
Granite in composition
How does rhyolite cool compared to granite?
Rhyolite cools more rapidly
What is pegmatite?
Very coarse-grained felsic rock
What minerals are commonly found in pegmatite?
Quartz, alkali feldspar, mica
What are the characteristics of granite?
Light coloured, medium to coarse-grained, intrusive igneous rock
What is granite primarily used for?
Dimension/building stones
What is the texture of granite?
Megascopic and microscopic characteristics
What is the appearance of granite?
Light coloured (leucocratic), medium to coarse-grained
What minerals primarily compose granite?
Quartz, alkali feldspar, plagioclase, mica, amphiboles, and other accessory minerals.
How does granite differ from granodiorite?
Granite has more alkali feldspar than plagioclase; granodiorite has more plagioclase than alkali feldspar.
What are the types of alkali feldspar found in granite?
Orthoclase and microcline.
What is the leucocratic nature of granite?
Granite is light-colored due to the dominance of light-colored minerals.
What colors can granite be found in?
Grey, white, red, or pink.
What is the quartz content in granite?
More than 20% quartz.
What is the alkali feldspar content in granite?
50-80% alkali feldspar.
What are the essential minerals in granite?
Alkali feldspar, Na-rich plagioclase, perthite, antiperthite, and quartz.
What are the accessory minerals in granite?
Muscovite, biotite, hornblende, zircon, apatite, titanite, tourmaline, topaz, ilmenite, and magnetite.
What are the secondary minerals found in granite?
Sericite, chlorite, and epidote.
What is the texture of granite?
Medium to coarse-grained, holocrystalline texture.
What is the typical grain size of granite?
Medium to coarse-grained.
What type of texture is commonly observed in granite?
Porphyritic texture.
What structures are commonly found in granite?
Xenoliths and rare foliations.
What is the appearance of granite?
Light colored rock composed mainly of light-colored minerals.
What is the typical arrangement of minerals in granite?
Irregular and compact arrangement.
What is the main composition of granite?
Quartz, alkali feldspar, plagioclase, mica
What is the dominant alkali feldspar in granite?
Microcline and orthoclase
What is perthite?
Intimate intergrowth of sodic and potassic feldspars
What does exsolution texture indicate?
Chemical breakdown of a homogenous solid solution during cooling
What are accessory minerals in granite?
Muscovite, biotite, hornblende, zircon, titanite, apatite, tourmaline, magnetite
What happens to feldspar during alteration?
Feldspar alters to sericite
What is the texture of granite?
Holocrystalline and hypidiomorphic
What is the granularity of granite?
Medium to coarse-grained
What is myrmekitic texture?
Intergrowth of quartz in plagioclase
What is graphic texture in granite?
Intergrowth of quartz and feldspar
What is monzogranite?
Granite with 35-65% alkali feldspar
What is syenogranite?
Granite with 65-90% alkali feldspar
What is alkali granite?
Granite with >90% alkali feldspar
What is the percentage of feldspar in granite?
65-90%
What is the alkali feldspar percentage in alkali granite?
90%
What mafic minerals are found in alkali granite?
Alkali pyroxenes (aegirineaugite) and alkali amphibole
What characterizes graphic granite?
Oriented intergrowth of quartz and orthoclase
What is Luxullianite?
Tourmaline-granite with significant tourmaline
What type of rock is granite classified as?
Felsic plutonic igneous rock
What type of rock is granite?
Intrusive igneous rock
In what forms does granite commonly occur?
Stocks, bosses, and batholiths
What is rhyolite?
A volcanic rock of felsic composition
What is the silica content of rhyolite?
68%
What is the alkali content in rhyolite?
Up to 5% (Na2O+K2O)
What temperature range do acidic lavas erupt at for rhyolite formation?
700 to 850°C
What are the dominant minerals in rhyolite?
Quartz (>20%), alkali feldspar (>35%), and biotite
What is a common appearance of rhyolite?
Fine-grained and often banded
What are the essential minerals in rhyolite?
K-feldspar (sanidine), Na-rich plagioclase, quartz, biotite
What are some accessory minerals in rhyolite?
Zircon, apatite, magnetite, ilmenite, pyroxene, amphibole
What are secondary minerals in rhyolite?
Sericite, chlorite
What is the texture of rhyolite?
Varies from glassy, aphanitic to porphyritic.
What reflects the lava flow direction in rhyolite?
Orientation of small crystals.
What type of grain size does rhyolite have?
Fine-grained, mostly aphanitic.
What is the common arrangement of constituents in rhyolite?
Equigranular and fine grained.
What structures can rhyolite have?
Vesicular or amygdaloidal structure.
What are spherulites in rhyolite?
Spherical bodies with radial aggregates of needles, usually quartz and feldspar.
What causes flow banding in rhyolite?
High viscosity and low capacity of rhyolitic lava flow.
What is a common texture observed in rhyolite?
Porphyritic texture.
What minerals compose rhyolite?
Quartz, sanidine, plagioclase, biotite, anorthoclase, magnetite.
What percentage of quartz is typically present in rhyolite?
More than 20%.
What are common accessory minerals in rhyolite?
Zircon, apatite, xenotime, pyroxene, amphibole, magnetite, ilmenite, rutile, leucoxene.
What characterizes the textures of obsidian and pumice?
Holohyaline and hypocrystalline textures.
What is the appearance of rhyolite under a microscope?
Varies from cryptocrystalline to microcrystalline felsitic type to porphyritic type.
What is commonly observed in rhyolite?
Sericitisation and chloritisation.
What type of texture is observed in devitrified glass portions of rhyolite?
Spherulitic texture.
What is the texture of devitrified glass portions?
Spherulitic texture
What characterizes obsidian?
Holohyaline and hypocrystalline textures
What is the crystallinity of rhyolite?
Mesocrystalline or hemicrystalline
What is the grain size of rhyolite?
Very fine and/or partly glassy
What texture may rhyolite exhibit?
Porphyritic texture
What are the phenocrysts found in rhyolite?
Quartz, plagioclase, orthoclase/sanidine
What shape are quartz phenocrysts?
Bipyramidal
What is obsidian?
Rhyolitic glass with 1-2% water content
What characterizes perlite?
Rhyolitic glass with 3-5% water content
What is pumice?
Highly vesicular glassy rhyolite
How are rhyolite rocks classified?
Felsic volcanic rocks
Where are rhyolites more common?
On continents than in oceans
What is the silica content range for intermediate rocks?
52 - 65%
What is the most common felsic mineral in intermediate rocks?
Plagioclase
What are common mafic minerals in intermediate rocks?
Hornblende, augite, biotite
What are common intermediate rocks?
Granodiorite, diorite, syenite, andesite, phonolite
What type of rocks are granodiorite, diorite, syenite, and andesite?
Intermediate rocks
What is granodiorite classified as?
Plutonic felsic rock
What color is granodiorite typically?
Light colored
What minerals dominate granodiorite?
Plagioclase over alkali feldspars
What is the grain size of granodiorite?
Medium to coarse-grained
What is the typical appearance of granodiorite?
Holocrystalline
What are the essential minerals in granodiorite?
Na-rich plagioclase, K-feldspar, quartz, biotite, amphibole
What accessory minerals are found in granodiorite?
Muscovite, apatite, magnetite, zircon
What secondary minerals are present in granodiorite?
Sericite, chlorite, epidote
What is the texture of granodiorite?
Holocrystalline texture
What type of structure is commonly found in granodiorite?
Layered structure
What is the dominant mineral in granodiorite under polarized light?
Plagioclase feldspar
What is the characteristic texture of granodiorite under microscopic examination?
Phaneritic texture
What is the dominant mineral in felsic rocks?
Feldspar and quartz
What type of rock is granodiorite classified as?
Felsic plutonic igneous rock
What is the typical texture of granodiorite?
Hypidiomorphic
What is the granularity of granodiorite?
Medium-grained to coarse-grained
What type of texture can granodiorite exhibit?
Porphyritic and granular
Which minerals are commonly found in granodiorite?
Quartz, feldspar, biotite, hornblende
What accessory minerals may be found in granodiorite?
Muscovite, zircon, titanite, apatite, tourmaline, magnetite
What alteration can feldspars undergo in granodiorite?
Alteration to sericite
Where does granodiorite typically occur?
In subduction zones and collisional settings
What is the volcanic equivalent of diorite?
Andesite
What is the composition of diorite?
Intermediate composition
What is the texture of diorite?
Granular texture
What is the relationship between granodiorite and tonalite?
Tonalite is a coarse-grained rock with less quartz and feldspars
Which minerals show pleochroism in granodiorite?
Hornblende and biotite
What type of twinning is observed in plagioclase?
Lamellar twinning
What is the volcanic equivalent of diorite?
Andesite
What is the mineral composition of diorite based on QAPF diagram?
More than 90% plagioclase, less than 5% quartz
What is diorite commonly referred to due to its appearance?
Salt and pepper rock
What is the typical color of diorite?
Dark to medium, speckled black and white
What type of rock is diorite classified as?
Medium-grained to coarse-grained holocrystalline intrusive igneous rock
What are the essential minerals in diorite?
Ca-Na plagioclase, amphibole, biotite, pyroxene
What are the accessory minerals found in diorite?
Minor quartz, alkali-feldspar, apatite, magnetite, garnet
What secondary minerals can be found in diorite?
Chlorite, sericite, epidote
What is the grain size of diorite?
Medium-grained to coarse-grained
What is the arrangement of minerals in diorite?
Irregular and compact
What are the main minerals present in diorite?
Plagioclase, amphiboles, biotite, quartz
What is the anorthite content of plagioclase in diorite?
Usually 50%
What does the presence of more quartz in diorite indicate?
The rock is termed as quartz diorite
What is the appearance of diorite under a microscope?
Laths of plagioclase with lamellar twinning and minor subhedral quartz
Which mafic minerals are commonly found in diorite?
Hornblende, augite, biotite
What are the main accessory minerals in diorite?
Magnetite, apatite, sphene, ilmenite, zircon
What type of quartz is present in diorite?
Minor amount of subhedral quartz
What mafic minerals dominate diorite?
Hornblende and augite
What is a characteristic feature of biotite in diorite?
Exhibits pleochroic haloes caused by zircon inclusions
What color can biotite in diorite range from?
Pale brown to dark brown
What interference colors can clinopyroxenes show?
Second order interference colours of blue and purple
What is the texture of diorite?
Holocrystalline and hypidiomorphic
What is the granularity of diorite?
Phaneritic with medium-sized crystals (1-2mm)
What types of rock are observed in diorite?
Quartzdiorite, Monzodiorite, Alkali diorite
What defines quartzdiorite?
Contains quartz (>5%) and alkali feldspar
What minerals are present in alkali diorite?
Ca-Na plagioclase, orthoclase-microcline, nepheline, sodalite, alkali amphibole, alkali pyroxene, biotite
What type of rock is diorite classified as?
Plutonic intermediate igneous rock
Where is diorite usually found?
Associated with subduction zones
What is syenite?
An intrusive plutonic rock belonging to the alkali series of intermediate igneous rock
What is the SiO2 content in syenite?
65% SiO2
What is the major mineral component of true syenite?
Alkali feldspar (orthoclase and/or microcline)
What is typically lacking in syenite?
Quartz
What are the volcanic equivalents of syenite?
Trachyte and phonolite
What is the color of syenite generally?
Varied, but mostly leucocratic
What is the mineralogical composition of syenite?
Alkali feldspar, plagioclase, amphibole, biotite, pyroxene
What accessory minerals can be found in syenite?
Quartz or feldspathoid, ilmenite, apatite, magnetite, zircon
What are feldspathoids?
Relatively rare minerals in syenitic rocks.
Can syenitic rock contain quartz?
No, syenitic rock with quartz cannot contain feldspathoids.
What are the secondary minerals found in syenite?
Chlorite and sericite.
What is the physical appearance of syenite?
Leucocratic, granular, holocrystalline rock.
What is the grain size of syenite?
Medium-grained to coarse-grained.
What type of texture does syenite exhibit?
Granular in nature, phaneritic texture.
What dominates the mineralogy of syenite?
Dominance of alkali feldspar.
What is the maximum percentage of quartz in syenite?
Cannot exceed more than 5%.
What types of alkali feldspar can be present in syenite?
Orthoclase and perthites, rarely microcline.
What are common accessory minerals in syenite?
Apatite, ilmenite, magnetite, and sulphides.
What type of texture shows syenite at the microscopic level?
Pandiomorphic and hypidiomorphic texture.
What are the two types of syenite?
Quartz syenite and nepheline syenite.
What characterizes quartz syenite?
Higher occurrence of quartz, Si-saturated variety.
What characterizes nepheline syenite?
Presence of nepheline, Si-undersaturated variety.
How is syenite classified?
As an intrusive plutonic intermediate rock.
Where are syenitic rocks usually found?
Associated with other plutonic rocks in small intrusive bodies.
What geological activities produce syenitic rocks?
Alkaline igneous activities from partial melting of lower crust.
In what geological settings are syenites formed?
Continental rift zones and subduction zones.
What are the most abundant igneous rocks on Earth?
Granite and granodiorite.
What type of rocks are most abundant in the Earth's crust?
Igneous rocks
What is the primary category of rocks found in the Earth's crust?
Igneous
What are important minerals in felsic rocks?
Quartz, feldspathoid, soda feldspar, potash feldspar, muscovite
What are the characteristics of granite?
Light coloured, medium to coarse-grained, intrusive igneous rock
What minerals primarily compose granite?
Quartz, alkali feldspar, plagioclase, mica, amphiboles, and other accessory minerals.
How does granite differ from granodiorite?
Granite has more alkali feldspar than plagioclase; granodiorite has more plagioclase than alkali feldspar.
What is the leucocratic nature of granite?
Granite is light-colored due to the dominance of light-colored minerals.
What are the essential minerals in granite?
Alkali feldspar, Na-rich plagioclase, perthite, antiperthite, and quartz.
What are the accessory minerals in granite?
Muscovite, biotite, hornblende, zircon, apatite, titanite, tourmaline, topaz, ilmenite, and magnetite.
What does exsolution texture indicate?
Chemical breakdown of a homogenous solid solution during cooling
What are accessory minerals in granite?
Muscovite, biotite, hornblende, zircon, titanite, apatite, tourmaline, magnetite
What mafic minerals are found in alkali granite?
Alkali pyroxenes (aegirineaugite) and alkali amphibole
What are the essential minerals in rhyolite?
K-feldspar (sanidine), Na-rich plagioclase, quartz, biotite
What are some accessory minerals in rhyolite?
Zircon, apatite, magnetite, ilmenite, pyroxene, amphibole
What are spherulites in rhyolite?
Spherical bodies with radial aggregates of needles, usually quartz and feldspar.
What are common accessory minerals in rhyolite?
Zircon, apatite, xenotime, pyroxene, amphibole, magnetite, ilmenite, rutile, leucoxene.
What is the appearance of rhyolite under a microscope?
Varies from cryptocrystalline to microcrystalline felsitic type to porphyritic type.
What are the essential minerals in granodiorite?
Na-rich plagioclase, K-feldspar, quartz, biotite, amphibole
What is the characteristic texture of granodiorite under microscopic examination?
Phaneritic texture
What accessory minerals may be found in granodiorite?
Muscovite, zircon, titanite, apatite, tourmaline, magnetite
What is the relationship between granodiorite and tonalite?
Tonalite is a coarse-grained rock with less quartz and feldspars
What is the mineral composition of diorite based on QAPF diagram?
More than 90% plagioclase, less than 5% quartz
What type of rock is diorite classified as?
Medium-grained to coarse-grained holocrystalline intrusive igneous rock
What are the accessory minerals found in diorite?
Minor quartz, alkali-feldspar, apatite, magnetite, garnet
What is the appearance of diorite under a microscope?
Laths of plagioclase with lamellar twinning and minor subhedral quartz
What is a characteristic feature of biotite in diorite?
Exhibits pleochroic haloes caused by zircon inclusions
What interference colors can clinopyroxenes show?
Second order interference colours of blue and purple
What minerals are present in alkali diorite?
Ca-Na plagioclase, orthoclase-microcline, nepheline, sodalite, alkali amphibole, alkali pyroxene, biotite
What is syenite?
An intrusive plutonic rock belonging to the alkali series of intermediate igneous rock
What is the mineralogical composition of syenite?
Alkali feldspar, plagioclase, amphibole, biotite, pyroxene
What accessory minerals can be found in syenite?
Quartz or feldspathoid, ilmenite, apatite, magnetite, zircon
What types of alkali feldspar can be present in syenite?
Orthoclase and perthites, rarely microcline.
What type of texture shows syenite at the microscopic level?
Pandiomorphic and hypidiomorphic texture.
Where are syenitic rocks usually found?
Associated with other plutonic rocks in small intrusive bodies.
What geological activities produce syenitic rocks?
Alkaline igneous activities from partial melting of lower crust.
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