Perthite
![Perthite, image taken of part of a feldspar grain in thin section as viewed with a petrographic microscope and a first-order red plate. The K-feldspar host (orthoclase) appears orange, and albite exsolution lamellae appear yellow. Long dimension of field is 0.4 mm.](/Images/godic/202412/21/Perthite_0.4mm0047.jpg")
![Megascopic antiperthite](/Images/godic/202412/21/Antiperthitic_feldspar0047.jpg")
![Perthite feldspar from Dan Patch pegmatite, Black Hills, South Dakota](/Images/godic/202412/21/Perthitic_feldspar_Dan_Patch_SD0047.jpg")
Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar (near K-feldspar, KAlSi3O8, in composition) includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar (near albite, NaAlSi3O8, in composition). Typically the host grain is orthoclase or microcline, and the lamellae are albite. If sodic feldspar is the dominant phase, the result is an antiperthite.