There are many variations of birthstones lists with much overlap and duplication between them.  We like this one.

                   COMMONLY   USED   BIRTHSTONES

               MONTH                      TRADITIONAL           MODERN

               January                        Garnet                        Garnet

               February                       Amethyst                    Amethyst

               March                            Bloodstone                Aquamarine 

               April                               Diamond                    Diamond

               May                               Emerald                     Emerald 

               June                              Alexandrite                 Pearl or Moonstone

               July                                Ruby                          Ruby 

               August                           Sardonyx                    Peridot

               September                     Sapphire                    Sapphire

               October                         Tourmaline                 Opal or Tourmaline

               November                     Citrine                         Yellow Topaz or

                                                                                        Citrine

               December                     Zircon or Lapis          Turquoise or Tanzanite