Perthite is the name given to an intergrowth of K-feldspar and albite-rich plagioclase that is produced by exsolution of the plagioclase from the potassium feldspar upon cooling of an original higher temperature, homogeneous solid solution of the two minerals.  There is a variety of terms applied to various textures of perthite, including “flame”, “patchy” and “lamellar”, describing the relationship of the two phases.  The term “perthite” applies to plagioclase in a K-spar host whereas “antiperthite” describes K-spar in a plagioclase host.  In the examples shown here, the two feldspars differ somewhat in degree of alteration.  In the large grain occupying the centre of the field in A and B, faintly twinned microcline hosts albite lamellae that are not seen to be twinned in this view.  In A, the lamellae are more cloudy that the host.  In C and D, patchy albite (with polysynthetic twinning visible in D) is hosted by untwinned K-feldspar, and in the plane light view (C), the K-feldspar appears more cloudy that the lamellae. A and B are from a granite from the Wopmay Orogen, NWT and C and D are from a granite from an unknown location.  Fields of view in A and B are 5.5 mm across and in C and D 2.2 mm across.  A and C ppl and B and D x-nicols.