Stress–strain behavior of the Rotokawa Andesite. Samples were subject to constant strain rate loading (1 × 10−5/s) and monitored for associated arbitrary acoustic emission energy output. All samples in this study display brittle failure. (A) Samples with low UCS generally develop a single fracture plane. (B) Samples near mean UCS develop several fracture planes. (C) Samples with very high UCS showed explosive, catastrophic failure into several large and small pieces with no distinct failure plane.