Terpene cyclase that catalyzes the cyclization of farnesyl diphosphate (FPP) to various sesquiterpenes, including alpha-muurolene, gamma-muurolene, germacrene, delta-cadinene, delta-cadinol and cubenol. (2E,6E)-farnesyl diphosphate = alpha-muurolene + diphosphate (2E,6E)-farnesyl diphosphate = diphosphate + gamma-muurolene (2E,6E)-farnesyl diphosphate = delta-cadinene + diphosphate The DDXXD motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.