Involved in the biosynthesis of phenolic monoterpenes natural products (PubMed:23624978). Monoterpene synthase which catalyzes the conversion of geranyl diphosphate (GPP) to alpha-terpineol (isomer is not determined) (PubMed:23624978). (2E)-geranyl diphosphate + H2O = (S)-alpha-terpineol + diphosphate (2E)-geranyl diphosphate + H2O = (R)-alpha-terpineol + diphosphate 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.