Well-formed crystals are prized by mineral specimen collectors because of their beauty and rarity. Uses of Feldspar ┗ Feldspar contains alumina, which results in an increase in the strength of the manufactured product. Orthoclase is a primary constituent of intrusive felsic igneous rocks such as granite, granodiorite, and syenites. They can sell for thousands of dollars. Feldspars (K Al Si 3 O 8 – Na Al Si 3 O 8 – Ca Al 2 Si 2 O 8) are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight.. Feldspars crystallize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Corrections? They are importantly dominant minerals in most igneous rock. Many metamorphosed limestones also contain anorthite. It can also occur in metamorphic rocks. Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Plagioclase, any member of the series of abundant feldspar minerals usually occurring as light-coloured, glassy, transparent to translucent, brittle crystals. Mafic igneous rocks (. Alkali feldspars are more commonly used commercially than plagioclase feldspars. Plagioclase is used in the manufacture of glass and ceramics; the iridescent varieties peristerite and labradorite are valued as gemstones or ornamental material. In the early 21st century Turkey led the world in feldspar production. Uses of Feldspar ┗ Feldspar contains alumina, which results in an increase in the strength of the manufactured product. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Andesine, less common, occurs in many granular and volcanic rocks with intermediate silica content, as in Marmato, Colombia, and Bodenmais, Bavaria, Germany. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... A scanning-electron-microscope photograph of pyroxene and plagioclase crystals (the long and the short crystals, respectively) that grew in a cavity in a fragment of Moon rock gathered during the Apollo 14 mission. Sanidine occurs as phenocrysts (large noticeable crystals) in extrusive felsic igneous rocks such as rhyolite and trachyte. Oligoclase, the most common plagioclase, occurs in granite, diorite, and other felsic igneous rocks and in some metamorphic rocks; notable occurrences are at Aust-Agder, Norway, and Fine, New York, United States. Our editors will review what you’ve submitted and determine whether to revise the article. Plagioclase refers to a series of silicate minerals in which the amount of sodium (Na) and calcium (Ca) varies. Silica is a major ingredient in refractories and whitewares. Feldspars are used widely in the glass and ceramics industries. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series. ┗ A bluish-green feldspar mineral is called amazonite. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. Strictly speaking,…, …are composed of hornblende and plagioclase. The role of silica is that of a filler, used to impart “green” (that is,…, Whitewares are often referred to as triaxial bodies, owing to the three mineral types—clay, silica, and feldspar—consistently found in their makeup. Feldspars are used widely in the glass and ceramics industries. With a Mohs hardness of 6 and perfect cleavage, these stones are usually considered to be too fragile for use in jewelry. Spectrolite is a trade name for labradorite with strong colour flashes. Albite is found commonly in granites, syenites, rhyolites, and trachytes. Omissions? Transparent material of high quality is also cut into faceted gemstones which are often sold as collector gems. Most of the crystals of the members of this series exhibit microscopic, repeated lamellar albite twinning; this produces the fine parallel striations observed on some surfaces. Basically, 50% rule says that Na dominant plagioclase is now albite and Ca dominant is anorthite. The chemical formulas vary from Na(AlSi3O8) to Ca(Al2Si2O8). However, the old plagioclases names are still used in petrology for classification of rocks. Flint (the…. Premium Membership is now 50% off. Feldspar also has a host of other end-uses which include urethane, mild abrasives, paints, welding of red coating, production of steel and latex foam. Three varieties have gemstone uses: Labradorite, Moonstone, and Sunstone. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. Certain feldspars are somewhat less common. …the alkali feldspars and the plagioclase feldspars. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Plagioclase is used in the manufacture of glass and ceramics; the iridescent varieties peristerite and labradorite are valued as gemstones or ornamental material. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. In contrast, andesine is rare except in andesites and diorites. Albite is common in pegmatites and may replace earlier formed microcline as cleavelandite. Therefore, this mineral is used … The alkali feldspars include orthoclase, microcline, sanidine, anorthoclase, and the two-phase intermixtures called perthite. ┗ Albite is an example of a feldspar that can be considered both, alkali as well as plagioclase. Microcline, also found in granitic rocks and pegmatites, is present in sedimentary rocks such as sandstones and conglomerates. Indirectly, the feldspar group provides some crucial resources that form as feldspars weather and break down. The rarest plagioclase is bytownite, which occurs in basic igneous rocks and in stony meteorites. Sunstone (oligoclase or orthoclase) is typically yellow to orange to brown with a golden sheen; this effect appears to be due to reflections from inclusions of red hematite. Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. … The chemical formulas vary from Na(AlSi3O8) to Ca(Al2Si2O8). Other uses of Potassium Feldspar Weathered potassium feldspars disintegrate into clay minerals and aluminum ores, both of which are important resources used in today’s society. They are major constituents in a wide range of intrusive and extrusive igneous rocks including granite, diorite, gabbro, rhyolite, andesite, and basalt. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. Alkali feldspars are more commonly used commercially than plagioclase feldspars. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium In addition, several feldspars are used as gemstones. Intermediate members are homogeneous mixtures of the pure end-members. It is usually added as quartz sand, sandstone, or flint pebbles. Anorthite is found only in gabbros, though it is common in certain high-grade metamorphic rocks such as granulite facies. Amazonite, a green variety of microcline, is used as an ornamental material. The feldspar-rich rocks larvikite and a few anorthosites are employed as both interior and exterior facing slabs. Let us know if you have suggestions to improve this article (requires login).

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