perthite
/ˈpəːθʌɪt/Geology
noun
A variety of alkali feldspar usually consisting of roughly parallel intergrowths of an exsolved sodium-rich phase (as albite) and a potassium-rich phase (as microcline).
Origin
Mid 19th century; earliest use found in Thomas Thomson. From Perth, the name of the town in Ontario, Canada, where it was first found + -ite.