The possible origin of the birthstone may come from a biblical reference to 'Aaron's breastplate' which was said to contain twelve gemstones; the specific gems are not known. Early people held many beliefs about the powers or curative effects of gems. The Victorians liked sentimental gifts and tokens; so, having a special birthstone was a popular idea.
The modern list was created in 1912. Citrine is a somewhat new addition to November and Tanzanite is a very new December addition, added in 2005. For the birthstone wearer there are no hard and fast requirements other than a love for gemstones.