Traditional birthstones are ones that have been the stones of choice for around about the last five hundred years. Many of the traditional birthstones, are the same ones that were used as ancient birthstones... depending on the culture and the area where the people were living... like the lovely purple Amethyst crystals.
As it became easier to obtain the stone... more were made available to the people. These days we can obtain crystals relatively easily, but it was not the same hundreds of years ago.
This is why they became regarded as very original gifts. Birthstones were often gemstones and were regarded as very special stones... to be given as gifts for occasions such as weddings and christenings.