The figure twelve appears to have been a favorite symbol with the ancients, who represented different objects or events by twelve different precious stones (now birthstones) as the tribes of Israel, the months of the year, and other subjects divided into the same number of parts.
Twelve gems engraved with anagrams of the name Jehovah, were employed by the Cabalists to predict zodiacal signs, and, under the Christian dispensation, different species were used to designate the twelve apostles, the Christian virtues, and other religious ideas.
The diamond symbolized life, joy, and innocence; the ruby, divine power and love; the sapphire, heaven, virtue, truth, and constancy; the emerald hope, faith, and victory; the amethyst, suffering, sorrow, love, peace, humility, purity, and modesty; the topaz, the goodness of God; the carbuncle, our Lord’s Passion».
It was these gems, that lately became known as birthstones.