The History of Birthstones
The idea of birthstones -- a gemstone assigned to each month of the year -- is thought to be an ancient one, and scholars trace it back to the Breastplate of Aaron described in the Bible in the book of Exodus. The Breastplate was a religious garment set with twelve gemstones that represented the twelve tribes of Israel. The gems were set in four rows of three: sardius, topaz and carbuncle; emerald, sapphire and diamond; ligure, agate and amethyst; and beryl, onyx and jasper.
So how did we get from gemstones representing the twelve tribes of Israel to birthstones? The writings of Flavius Josephus (1st century AD) and St. Jerome (fifth century AD) made the connection between the 12 stones in the Breastplate and the 12 signs of the zodiac. The idea was proposed that each of the gemstones had special powers associated with the corresponding astrological sign, and that wearing these stones at the right time would have therapeutic or talismanic benefits.
But this was not quite the same idea as our concept of the birthstone. Based on this astrological model, one ought to own a collection of the 12 different gemstones assigned to the signs of the zodiac, and wear the appropriate gem during the ascendancy of the corresponding sign. This is more like the Vedic astrological tradition of India, which assigns 9 different gemstones to 9 planets, and prescribes the wearing of particular gems according to your health and the challenges you face in your life. The idea of each person always wearing a gemstone corresponding to the month of his or her birth is a distinctly modern idea that scholars trace to 18th century Poland, with the arrival of Jewish gem traders in the region. But the modern list of birthstones was not defined until 1912, by the National Association of Jewelers (Jewelers of America) in the USA.
What's the difference between a mineral and a gem?
All birthstones are minerals, but why are some minerals considered gems? Interestingly, there is no geological definition for the word gem, because a gem is a human creation. Minerals are formed by geologic processes in rocks in their natural environment. When we excavate precious or semiprecious stones, cut, and polish them into specific shapes, they become gems. When a gem is set into metal to be worn on the body it becomes a jewel. Several key factors determine the value of a gem: To be considered worthy of jewelry, the mineral must have rarity, durability, attractiveness, size, and color.