Single-crystal perthite maximum microcline was shocked to a peak pressure of 417 kbar in a series of 15 recovery experiments. Shock-induced cleavagelike lamellar features parallel to {1¿11} and {111¿} form above 50 kbar and contain diaplectic glass at higher shock pressures. Sets of planar deformation features parallel to specific crystallographic planes are developed above 150 kbar; some orientations transform to deformation twins above 200 kbar. With increasing pressure, bulk density, refractive indices, and birefringence of the recovered material decrease and approach diaplectic glass values: disappearance and weakening of reflections in Debye-Scherrer patterns are due to disordering of the feldspar lattice. In experiments above 300 kbar the X ray pattern is that of a previously unrecorded disordered phase which possibly inverted from a compressed phase on pressure release. Weak indications of jadeite and stishovite may be remnants of the high-pressure breakdown of albite stringers.