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. 5. Orthoclase, also known as alkali feldspar or K-feldspar, is one end-member of a solid solution between orthoclase and albite. Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite. The Plagioclase series is a group of related feldspar minerals that essentially have the same formula but vary in their percentage of sodium and calcium. Albite and Anorthite are the end members of the series, with the intermediary minerals Oligoclase, Andesine, Labradorite, and Bytownite. The mineral is a component in igneous rocks, and it is a tectosilicate mineral as well. With the 50% rule, all of the mineral members occuring between these two are not considered valid minerals by IMA. Orthoclase Orthoclase is a member of the feldspar group (like plagioclase) and is a framework silicate. In summary, the orthoclase is an important mineral in the feldspar group, and the chemical formula of the mineral is KAlSi3O8 while plagioclase is an important mineral in the feldspar group, and the chemical formula of this mineral is NaAlSi3O8– CaAl2Si2O8. Moreover, the crystal system of orthoclase is monoclinic while in plagioclase, it is triclinic. Plagioclase Plagioclase is a member of the feldspar group (like orthoclase) and is a framework silicate. 2. In plagioclase the orthoclase component is usually at very low concentrations. orthoclase crystals grew and later inverted to microcline. Orthoclase is a common constituent of most granites and other felsic igneous rocks and often forms huge crystals and masses in pegmatite. Plagioclase is usually white to light gray in color, although color is not a reliable mineral indicator. Orthoclase crystals and twins provide information on the formation of minerals and environmental factors. The key difference between orthoclase and plagioclase is that orthoclase appears in green-yellow colour, whereas plagioclase appears in white. Moreover, this mineral is mostly transparent or translucent. Typically, the pure potassium endmember of orthoclase forms a solid solution with albite, the sodium endmember (NaAlSi 3 O 8), of plagioclase. K-feldspar crystals are typically tabular and often elongate. 1. Orthoclase and plagioclase are important minerals. It is also a tectosilicate mineral. The following table shows their compositio… The composition of a plagioclase feldspar is typically denoted by its overall fraction of anorthite (%An) or albite (%Ab), and readily determined by measuring the plagioclase crystal's refractive index in crushed grain mounts, or its extinction angle in thin section under a polarizing microscope. The Mohs scale harness of orthoclase is 6.0. This was first shown by the German mineralogist Johann Friedrich Christian Hessel (1796–1872) in 1826. Side by Side Comparison – Orthoclase vs Plagioclase in Tabular Form 2. 1. 4b in The biotite has a pebbly texture and micaceous cleavage.The right half of the view contains a large grain of clear to cloudy K-feldspar. More definitive in distinguishing plagioclase from orthoclase is the presence of fine parallel lines called "striations" on plagioclase - these striations do not occur with orthoclase. However, the mineral streak of orthoclase is white. The peristerite, Bøggild and Huttenlocher intergrowths are lamellar intergrowths (Fig.2) believed to form on solvus curves. As nouns the difference between orthoclase and plagioclase is that orthoclase is (mineralogy) potassium]] aluminum silicate, kalsi 3 [[oxygen|o 8, a common feldspar of igneous, plutonic, and metamorphic rocks orthoclase is the main feldspar of pegmatite occurrences, where it is most commonly flesh-colored orthoclase is used in the ceramic and glass industries and as a decorative gravel while plagioclase is … K-feldspar, Quartz and Biotite in a Granite. Moreover, this mineral is a common component in many granite forms. 4b in The plagioclase group consists of albite-anortite series of feldspars. It has a pearly lustre on cleavage surfaces. This subtraction eventually creates nano-sized holes (Fig. 4a and Fig. Orthoclase is found in silica-rich igneous rocks such as granite, and in high grade metamorphic rocks. Moreover, the crystal system of orthoclase is monoclinic while in plagioclase, it is triclinic. It has a vitreous lustre and the mineral streak is white. “PlagioclaseFeldsparUSGOV” (Public Domain) via Commons Wikimedia. Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. *:These crystals are of one of the most abundant minerals in nature – feldspar; furthermore, they are of a particular kind of feldspar rich in the element calcium, termed. Terms of Use and Privacy Policy: Legal. Compare the Difference Between Similar Terms. With a mind rooted firmly to basic principals of chemistry and passion for ever evolving field of industrial chemistry, she is keenly interested to be a true companion for those who seek knowledge in the subject of chemistry. What is Plagioclase Basically, 50% rule says that Na dominant plagioclase is now albite and Ca dominant is anorthite. “Orthoclase Feldspar.” Geology, Available here. Plagioclase is not actually a rock, but a member of the feldspar family of minerals, and a major rock forming silicate mineral. The material is either transparent or translucent. With very rare exceptions they are on sub-micrometre scales and not visible in an optica lmicroscope. Appearance and habit - Microcline and orthoclase are generally anhedral; sanidine is more likely to form euhedral phenocrysts. You can find more details on the difference between orthoclase and plagioclase in the below infographic. The extinction angle is an optical characteristic and varies with the albite fraction (%Ab). The key difference between orthoclase and plagioclase is that orthoclase appears in green-yellow colour, whereas Plagioclase appears in white colour. The key difference between orthoclase and plagioclase is that orthoclase appears in green-yellow colour, whereas plagioclase appears in white. When considering the uses of orthoclase, it is important in the manufacture of some glass and ceramics, e.g. See Wiktionary Terms of Use for details. 3. During early alterations of deformed plagioclase in the diorite, disruption of zoning and disappearance of albite-twinning occur as Ca and some Al are subtracted from the plagioclase lattice. Orthoclase is an important mineral in the feldspar group, and the chemical formula of this mineral is KAlSi3O8. Subgroup orthoclase and albite constitut: Orthoclase (K-feldspar) Subgroup albite and anorthite constitut: Plagioclase The mixed crystal groups between the two end joints albite (sodium feldspar), NaAlSi3O8) and anorthite (lime feldspar, CaAl2Si2O8) constitutes plagioclase that usually can be separated from alkali feldspar by distinctive twin striping on the cleaving surfaces. Summary. Furthermore, it is an important component in scouring powder. Where is orthoclase found? Creative Commons Attribution/Share-Alike License; (mineralogy) Potassium]] aluminum silicate, KAlSi. Madhu is a graduate in Biological Sciences with BSc (Honours) Degree and currently persuing a Masters Degree in Industrial and Environmental Chemistry. Plagioclase Orthoclase: Feldspar is a name given to a class of aluminum-containing silicates which are sometimes called light silicates or "nonferromagnesian silicates" since they don't contain iron or magnesium. Also, this mineral is important as a gemstone; for example, moonstone, which mainly contains orthoclase, is an important gemstone. This appears as a green-yellow solid. All rights reserved. Plagioclase is an important mineral in the feldspar group, and the chemical formula of this mineral is NaAlSi3O8– CaAl2Si2O8. Text is available under the Creative Commons Attribution/Share-Alike License; additional terms may apply. The crystal system of this mineral is monoclinic. The key difference between orthoclase and plagioclase is that orthoclase appears in green-yellow colour, whereas plagioclase appears in white colour. 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orthoclase vs plagioclase

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