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Mineral

Feldspar

Silicate Minerals

Feldspar is a group of rock-forming aluminium tectosilicate minerals that also contain sodium, calcium, potassium or barium. The most common members are the plagioclase feldspars, a sodium and calcium series, and the alkali feldspars, which hold potassium and sodium. Feldspars make up about 60 percent of the Earth's crust, crystallize from magma as both intrusive and extrusive igneous rocks, and are present in many metamorphic and sedimentary rocks. Their compositions are described by three end members: orthoclase, albite and anorthite. Chemical weathering turns feldspar into clay minerals such as illite, smectite and kaolinite, which is why it is usually not prevalent in sedimentary rocks. Feldspar is also a common raw material in glassmaking and ceramics. The name comes from the German Feldspat, from Feld meaning field and Spat meaning flake.

Facts
Formation Class
Framework silicate, the most abundant mineral group in the Earth's crust 2
Chemical Formula
KAlSi3O8 - NaAlSi3O8 - CaAl2Si2O8 (end-member series) 1
Hardness (Mohs)
6 2
Standard reference value for the feldspar group generally; individual species vary slightly.
Colour
Colourless or White 3
Colour
Grey or Black 3
Colour
Brown 3
Colour
Red or Pink 3
Colour
Orange or Yellow 3
Colour
Green 3
Colour
Blue or Purple 3
Lustre
Vitreous 3
Lustre
Pearly 3
Rarity
Abundant 3
Classification
Strunz Class
Silicates 1
Use
Ceramic and Glass Manufacture 1
Connections

Associated With

Amphibolite, Materials

Plagioclase feldspar is one of the two defining minerals of amphibolite, alongside amphibole.

Granite, Materials

Granite's own lead description names alkali feldspar as one of its main constituent minerals.

Source Granite (Wikipedia)
Migmatite, Materials

The pale leucosome bands of a migmatite are quartzofeldspathic melt segregations.

Monzonite, Materials

Monzonite is defined by roughly equal plagioclase and alkali feldspar with little quartz.

Pegmatite, Materials

Feldspar named as one of the three dominant minerals of most pegmatites.

Source Pegmatite (Wikipedia)
Rhyolite, Materials

Sanidine and plagioclase are both feldspar-group minerals; feldspar is a principal mineral of rhyolite.

Source Rhyolite (Wikipedia)
Trachyte, Materials

Trachyte is defined by its dominant alkali feldspar content.

Caused By

Fractional Crystallization, Processes
Source EBSCO Research Starters: Igneous processes, rocks, and mineral deposits
Additional Source Feldspar (Wikipedia)Compositions
Magmatism, Processes
Source Feldspar (Wikipedia)
Volcanism, Processes
Source Feldspar (Wikipedia)

Classified As

Silicate Minerals, Subcategories

In Discipline

Mineralogy, Disciplines
Source Mineral (Wikipedia)
Sources
1. Feldspar (Wikipedia)
Wikimedia Foundation
  • Article text
    Compositions of major elements in common feldspars can be expressed in terms of three endmembers: orthoclase endmember KAlSi3O8 albite endmember NaAlSi3O8 anorthite endmember CaAl2Si2O8 Solid solutions between orthoclase and albite are called alkali feldspar.
  • Lead section, third sentence
    Feldspars make up about 60% of the Earth's crust and 41% of the Earth's continental crust by weight.
  • Lead section
    Feldspar ( 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.
  • Feldspar (Wikipedia), Applications section
    Feldspar is a common raw material used in glassmaking, ceramics
  • Caused By: Fractional Crystallization, Compositions
    Calcium-rich plagioclase is the first feldspar to crystallize from cooling magma, then the plagioclase becomes increasingly sodium-rich as crystallization continues.
  • Caused By: Magmatism, Lead
    Feldspars crystallize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock.
View the Source
2. Mineral (Wikipedia)
Wikimedia FoundationView the Source
3. Geology.com: Feldspar
Geology.com
  • Color field
    Usually white, pink, gray or brown. Also colorless, yellow, orange, red, black, blue, green.
  • Luster field
    Vitreous. Pearly on some cleavage faces.
  • Description
    The most abundant group of minerals in Earth's crust.
View the Source
Wikidata: Feldspar
Wikidata Q170258
Granite (Wikipedia)
Wikimedia FoundationAssociated With: Granite, Lead section
Quote, Associated With: Granite, Lead section
is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, mica and plagioclase.
View the Source
Rhyolite (Wikipedia)
Wikimedia FoundationAssociated With: Rhyolite, Mineralogy section
Quote, Associated With: Rhyolite, Mineralogy section
The mineral assemblage is predominantly quartz, sanidine, and plagioclase.
View the Source
Pegmatite (Wikipedia)
Wikimedia FoundationAssociated With: Pegmatite, Lead section
Quote, Associated With: Pegmatite, Lead section
Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite.
View the Source
EBSCO Research Starters: Igneous processes, rocks, and mineral deposits
EBSCO Research StartersCaused By: Fractional Crystallization, Pegmatites and hydrothermal fluids
Quote, Caused By: Fractional Crystallization, Pegmatites and hydrothermal fluids
The high water content of pegmatite fluids, some of it occurring as vapor, allows minerals such as quartz, feldspar, and mica to grow to enormous sizes, the largest of which are on the order of railway boxcars.
View the Source
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