In Mesopotamia, ancient Egyptians began to draw parallels between colored gemstones and the celestial lights. Each individual gemstone was assigned to a different planet of the sun. Life on earth, and the twinkle of gemstones, were thought to be connected to the twinkle of the stars.
The Chaldeans, the last peoples to rule Mesopotamia, made a chart, linking each gemstone with one of the planets. It read like this:
The ancient Greeks also assigned different stones to particular stars. They revered the times when the sun appeared in one of the twelve major constellations and assigned each particular gemstone to each constellation. These assignments were based on a few different factors; the color of the gem, and the associations the color had, the supposed powers each gem possessed, as well as the powers and colors associated with each sign.
In the beginning, it seems that every person who could afford to, bought one of each of the twelve stones, and wore each stone in correspondence with its particular month, in the belief that during that month, the stone would be the most powerful. After a while however, this practice ended, and the practice of only wearing the stone associated with his or her particular zodiac sign began.