In vitro, catalyzes the formation of 1,8-cineole from geranyl diphosphate (GPP) (PubMed:21726035, PubMed:28144299, PubMed:28966840). Can also accept neryl diphosphate (NPP) as substrate to produce 1,8-cineole (PubMed:28966840). (2E)-geranyl diphosphate + H2O = 1,8-cineole + diphosphate H2O + neryl diphosphate = 1,8-cineole + diphosphate Binds 3 Mg(2+) ions per subunit. kcat is 0.079 sec(-1) with geranyl diphosphate (GPP) as substrate. Homodimer. The Asp-Asp-Xaa-Xaa-Asp (DDXXD) and Asn-Xaa-Xaa-Xaa-Ser-Xaa-Xaa-Xaa-Glu (NSE) motifs are important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.