- The fracture properties of glass ceramic induced by compression were investigated by combined electromagnetic radiation (EMR) and fractographic methods. The study of a transparent sample enabled us to elucidate the sequence of crack nucleation, growth and interaction, and the ultimate longitudinal splitting under incremental increase of uniaxial stress in five stages. The fracture process was accompanied by some 18 EMR pulses. The short EMR pulses (of a duration of 0. 8–1.5 μs) occur under low stresses (0.36–1.7 MPa) in association with microcracking at the sample outer surface. Medium pulses (durations of 15–25 μs) are associated with stresses of up to 65 MPa and are correlated with crack limited growth outside the specimen. A lengthy pulse (duration of more than 40 μs) occurs under greater stresses (112 MPa) and correlates with the longitudinal splitting at failure. A return to the 17–20 μs range occurs for the post-failure cracking during stress relaxation.