Involved in the biosynthesis of phenolic monoterpenes natural products (PubMed:23246843). Monoterpene synthase which catalyzes the conversion of geranyl diphosphate (GPP) to sabinene hydrate, mainly (Z)-sabinene hydrate and to a lower extent (E)-sabinene hydrate, and the formation of minor amounts and traces of several other monoterpenes (e.g. mainly alpha-thujene, alpha-pinene and myrcene) (PubMed:23246843). (2E)-geranyl diphosphate + H2O = diphosphate + sabinene hydrate Binds 3 Mg(2+) or Mn(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Homodimer. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.