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Omphacite is the solid solution of Fe-bearing diopside (CaMgSi<sub>2</sub>O<sub>6</sub>) and jadeite (NaAlSi<sub>2</sub>O<sub>6</sub>). Depending on how much the coupled substitution of (Na, Al)-(Mg-Fe, Ca) happens, the [[chemical composition]] of omphacite varies continuously from pure diopside to pure jadeite.<ref name=":1" /> Due to the relatively small radius of (Na, Al) atoms, the [[Unit Cell|unit cell]] volume linearly decreases as jadeite component increases.<ref name=":2">{{Cite journal|last1=Pandolfo|first1=Francesco|last2=Cámara|first2=Fernando|last3=Domeneghetti|first3=M. Chiara|last4=Alvaro|first4=Matteo|last5=Nestola|first5=Fabrizio|last6=Karato|first6=Shun-Ichiro|last7=Amulele|first7=George|date=2015|title=Volume thermal expansion along the jadeite–diopside join|url=https://doi.org/10.1007/s00269-014-0694-9|journal=Physics and Chemistry of Minerals|language=en|volume=42|issue=1|pages=1–14|doi=10.1007/s00269-014-0694-9|bibcode=2015PCM....42....1P|hdl=2318/153763 |s2cid=96677363|issn=1432-2021|hdl-access=free}}</ref> In addition, the coupled substitution also stiffens the crystals. The [[Bulk modulus|bulk]] and [[Shear modulus|shear]] modulus linearly increases as jadeite component increases.<ref name=":1" />
== Space
Although omphacite is the solid solution of [[diopside]] and [[jadeite]], its [[space group]] may be different with them. The space group of diopside and jadeite is C2/c. However, omphacite can show both P2/n and C2/c space group. At low temperature, the partial coupled substitution of (Na, Al)-(Mg-Fe, Ca) in omphacite orders the atoms in the unit cell and makes omphacite shows a relatively low symmetry space group P2/n.<ref>{{Cite journal|last1=Skelton|first1=Richard|last2=Walker|first2=Andrew M.|date=2015|title=The effect of cation order on the elasticity of omphacite from atomistic calculations|url=https://doi.org/10.1007/s00269-015-0754-9|journal=Physics and Chemistry of Minerals|language=en|volume=42|issue=8|pages=677–691|doi=10.1007/s00269-015-0754-9|bibcode=2015PCM....42..677S|s2cid=92245503|issn=1432-2021}}</ref> As temperature increases, the movements of the atoms increase and finally the coupled substitution will not influence the order of the structure. When temperature reaches ~
Although the atomic positions in the two space groups have a subtle difference, it
== Etymology and history ==
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