Our observations of the microcracks in a small suite of samples of amphibolite and granulite facies rocks of variable composition show that (1) most cracks are partly or completely sealed, (2) the minerals that seal microcracks are unrelated to phase equilibria associated with granulite facies metamorphic conditions, and (3) the present crack porosity is related to bulk composition rather than to metamorphic grade. All observed cracks (open, healed, sealed) appear to have formed in response to tectonic stresses associated with retrograde metamorphism.