Dynamic fatigue data are reported for fine- and coarse-grained micaceous glass-ceramics after contact damage with spheres. The strengths of indented specimens are measured at stressing rates from similar to 10(-2) to 10(4) MPa.s(-1) in water. The strength degradation is substantially faster in the coarse-grained structure, and is accelerated further by multicycle contact loading. Failures originate from contact sites in all cases but undergo a progressive transition from classical cone cracks to quasi-plastic microcrack zones with increases in the grain size and the number of contact cycles. The results highlight the particularly deleterious effect of quasi-plastic damage accumulation on lifetime.