Perthite

An intergrowth of albite or oligoclase with a microcline host, occasionally also with an orthoclase host. The intergrowths or exsolution lamellae of the albite are visible as white lines coursing through the K feldspar groundmass. Common in granite pegmatites. See also microperthite. Originally described from North Burgess, Drummond Township, Lanark Co., Ontario, Canada.