(NaAlSi₃O₈) in pink microcline. The intergrowths in perthite have a great variety of shapes. If cooling is sufficiently slow, the alkali feldspar may exsolve to form separate grains with near-endmember albite and K-feldspar compositions. The largest documented single crystal of perthite was found in Hugo Mine in South Dakota and measured about 10.7 m × 4.6 m × 1.8 m.

The gem varieties of potassium feldspar, amazonite