Fig. 22. Replacement of K-feldspar (gray) in perthite by tertiary plagioclase (albite-twinned albite; dark) leave secondary plagioclase lamellae (cream) of the former perthite as optically continuous islands in the tertiary plagioclase. Note adjacent plagioclase (cream white) also replaces K-feldspar in perthite (bottom right) with remnant plagioclase lamellae (tan) projecting into the plagioclase (cream white).