Feldspar crystal 18 cm × 21 cm × 8.5 cm (7.1 in × 8.3 in × 3.3 in) from Jequitinhonha valley, Minas Gerais, southeastern Brazil
General
Category
Tectosilicate
Formula (repeating unit)
KAlSi 3O 8 – NaAlSi 3O 8 – CaAl 2Si 2O 8
IMA symbol
Fsp[1]
Crystal system
Triclinic or monoclinic
Identification
Color
pink, white, gray, brown, blue
Cleavage
two or three
Fracture
along cleavage planes
Mohs scale hardness
6.0–6.5
Luster
Vitreous
Streak
white
Diaphaneity
opaque
Specific gravity
2.55–2.76
Density
2.56
Refractive index
1.518–1.526
Birefringence
first order
Pleochroism
none
Other characteristics
exsolution lamellae common
References
[2]
Compositional phase diagram of the different minerals that constitute the feldspar solid solution
Feldspar (/ˈfɛl(d)ˌspɑːr/FEL(D)-spar; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium.[3] The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars.[4] Feldspars make up about 60% of the Earth's crust,[3] and 41% of the Earth's continental crust by weight.[5][6]
Feldspars crystallize from magma as both intrusive and extrusive igneous rocks[7] and are also present in many types of metamorphic rock.[8] Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite.[9] Feldspars are also found in many types of sedimentary rocks.[10]
^"Feldspar". Gemology Online. Retrieved 8 November 2012.
^ abNeuendorf, K.K.E.; Mehl, J.P. Jr.; Jackson, J.A., eds. (2005). Glossary of Geology (5th ed.). Alexandria, Virginia: American Geological Institute. p. 232. ISBN 978-0922152896.
^Deer, W.A; Howie, R.A.; Zussman, J. (2001). Rock-forming Minerals (2nd edition) Volume 4A. London: Geological Society of London. p. 2. ISBN 1-86239-081-9.
^Anderson, Robert S.; Anderson, Suzanne P. (2010). Geomorphology: The Mechanics and Chemistry of Landscapes. Cambridge University Press. p. 187. ISBN 9781139788700.
^Rudnick, R. L.; Gao, S. (2003). "Composition of the Continental Crust". In Holland, H. D.; Turekian, K. K. (eds.). Treatise on Geochemistry. Vol. 3. New York: Elsevier Science. pp. 1–64. Bibcode:2003TrGeo...3....1R. doi:10.1016/B0-08-043751-6/03016-4. ISBN 978-0-08-043751-4.
^TROLL, V. R. (2002-02-01). "Magma Mixing and Crustal Recycling Recorded in Ternary Feldspar from Compositionally Zoned Peralkaline Ignimbrite A', Gran Canaria, Canary Islands". Journal of Petrology. 43 (2): 243–270. Bibcode:2002JPet...43..243T. doi:10.1093/petrology/43.2.243. ISSN 1460-2415.
^"Metamorphic Rocks." Metamorphic Rocks Information Archived 2007-07-01 at the Wayback Machine. Retrieved on July 18, 2007
^Blatt, Harvey and Tracy, Robert J. (1996) Petrology, Freeman, 2nd ed., pp. 206–210 ISBN 0-7167-2438-3
^"Weathering and Sedimentary Rocks." Geology. Archived 2007-07-03 at the Wayback Machine Retrieved on July 18, 2007.
common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars make up about 60%...
Potassium feldspar refers to a number of minerals in the feldspar group, and containing potassium: Orthoclase (endmember formula KAlSi3O8), an important...
(phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and...
Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient...
Alkali feldspar granite, some varieties of which are called 'red granite', is a felsic igneous rock and a type of granite rich in the mineral potassium...
is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical...
20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar, because they are the most resistant minerals to the weathering processes...
Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters...
type Andesite – Type of volcanic rock Alkali feldspar granite – Type of igneous rock rich in alkali feldspar Anorthosite – Mafic intrusive igneous rock...
igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in...
holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or pink, and in general appearance...
Sunstone is a microcline or oligoclase feldspar, which when viewed from certain directions exhibits a spangled appearance. It has been found in Southern...
intergrowths are associated with and commonly in contact with potassium feldspar. Myrmekite is formed under metasomatic conditions, usually in conjunction...
subsolvus or two feldspar granites crystallisation occurs at high water pressures resulting in the formation of two types of feldspar as opposed to hypersolvus...
describing igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are relatively richer...
rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various...
sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite. However, rarer...
a metamorphic rock that is altered granite composed of pink orthoclase feldspar, green epidote, and generally colorless quartz. It was first found in the...
alkali metal oxides. Monzonite is composed mostly of plagioclase and alkali feldspar. Syenodiorite is an obsolescent term for monzonite or for monzodiorite...
crystals of feldspar. These feldspars are known as ternary because they contain significant components of all three endmember feldspars. The feldspar has partly...
USS Feldspar (IX-159), a Trefoil-class concrete barge designated an unclassified miscellaneous vessel, was the only ship of the United States Navy to be...
total content of quartz, alkali feldspar, and plagioclase (QAPF) and alkali feldspar makes up 35% to 90% of its total feldspar content. Feldspathoids are not...
minerals; a granite is defined by proportions of quartz, alkali feldspar, and plagioclase feldspar. The other minerals in the rock are termed accessory minerals...
type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose...
a single feldspar as opposed to subsolvus granites in which two distinct types of feldspar are present. The distinctive character of feldspar in hypersolvus...
syenite is trachyte. The feldspar component of syenite is predominantly alkaline in character (usually orthoclase). Plagioclase feldspars may be present in small...
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