:''Pericline also refers to a doubly plunging

anticline In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...

or syncline.'' Pericline is a form of

albite Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilicate ...

exhibiting elongate prismatic crystals. Pericline twinning is a type of

crystal twinning Crystal twinning occurs when two or more adjacent crystals of the same mineral are oriented so that they share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals that are tightly ...

which show fine parallel twin laminae typically found in the alkali feldspars

microcline Microcline (KAlSi3O8) is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during slo ...

. The twinning results from a structural transformation between high temperature and low temperature forms.Tsatskis, I. and E.K.H. Salje (1996) ''Time evolution of pericline twin domains in alkali feldspars'', American Mineralogist, Volume 81, pages 800-81
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References

Crystallography Tectosilicates {{silicate-mineral-stub