Supernatural powers have been attributed to objects since ancient times. Gemstones—precious and semi-precious—have been so assigned by astrologers and magicians for thousands of years. The Greeks and Romans believed that there was a force inherent in the stones.
The particular power attributed to a stone is usually based on the stone's color. For this reason there are frequently a number of different stones equally useful for various purposes. For example, in gem therapy ruby, garnet, and red coral would all be useful for the heart and for blood circulation and stimulation, as their red color corresponds to that of blood. Because blue is believed to having a calming effect, sapphire, beryl, lapis lazuli, were used against fevers.
Stones are also associated with birth dates and, as birthstones, are believed to have potency for those people born under their particular zodiacal sign. To carry your birthstone is to ensure good luck, health and prosperity. Medieval astrology established such a relationship, although the particulars have been changed over the years to accommodate availability of the stones, their cost, and even their popularity.
Originally it was suggested that the stones corresponded to those on the Breastplate of Aaron, the Jewish High Priest, but this does not hold up under scrutiny. The twelve stones were also said to represent the twelve tribes of Israel, the twelve months of the year, and the twelve signs of the zodiac, and were set in four rows of three. According to the instructions given in Exodus 28:17-20, the stones were arranged as follows: Sardius, Topaz, and Carbuncle in the first row; Emerald, Sapphire, and Diamond in the second; Ligure, Agate, and Amethyst in the third; and Beryl, Onyx, and Jasper in the fourth. But these names do not necessarily equate with the names used today. For example, the "sapphire" of the Bible was more probably lapis lazuli rather than what we now know as sapphire, and "diamond" was probably what we now know as white topaz.
Birthstones, then, are not constant; they change over the generations. Here are the associations according to some magicians and Witches:
| Aries | Ruby, Bloodstone, Red Jasper |
| Taurus | Golden Topaz, Coral, Emerald |
| Gemini | Crystal, Carbuncle, Aquamarine |
| Cancer | Emerald, Moonstone |
| Leo | Ruby, Sardonyx, Amber |
| Virgo | Pink Jasper, Turquoise, Zircon |
| Libra | Opal, Diamond |
| Scorpio | Agate, Garnet, Topaz |
| Sagittarius | Amethyst |
| Capricorn | Black-and-white Onyx, Beryl, Jet |
| Aquarius | Blue Sapphire |
| Pisces | Diamond, Jade |
If you wish to be directed by the day of the week on which you were born, then the following are the gems associated with the days:
| Sunday | Gold and Yellow gems |
| Monday | Pearls and all white stones |
| Tuesday | Rubies and all red stones |
| Wednesday | Turquoise, Sapphire, and all blue stones |
| Thursday | Amethyst and all purple stones |
| Friday | Emerald and all green stones |
| Saturday | Diamond, also black stones |
David and Julia Parker give the following, as the stones associated with the zodiac signs:
| Aries | Diamond |
| Taurus | Sapphire |
| Gemini | Agate |
| Cancer | Pearl |
| Leo | Ruby |
| Virgo | Sardonyx |
| Libra | Sapphire |
| Scorpio | Opal |
| Sagittarius | Topaz |
| Capricorn | Turquoise |
| Aquarius | Amethyst |
| Pisces | Moonstone |
To complicate the issue, many authorities give the calendar months rather than the zodiacal signs. For example, Arthur Edward Waite, writing as "Grand Orient" in The Book of Destiny (University Books, 1972) gives the following:
| January | Garnet, Zircon |
| February | Pearl, Amethyst |
| March | Jasper, Ruby |
| April | Diamond, Sapphire |
| May | Aquamarine |
| June | Agate |
| July | Ruby, Cornelian |
| August | Moonstone, Sardonyx |
| September | Chrysolite, Sapphire |
| October | Opal |
| November | Topaz |
| December | Malachite, Turquoise |
The Encyclopedia Britannica agrees on some of these, giving a table of both traditional and modern stones:
| Month | Traditional | Modern | Synthetic |
|---|---|---|---|
| January | Garnet | Garnet | |
| February | Amethyst | Amethyst | |
| March | Bloodstone | Aquamarine | Aquamarine |
| April | Diamond | White Sapphire | |
| May | Emerald | Emerald | Emerald |
| June | Pearl | Alexandrite | Cultured Pearl |
| July | Ruby | Ruby | August |
| August | Sardonyx | Peridot | Peridot |
| September | Sapphire | Sapphire | |
| October | Opal | Tourmaline | Rozircon (pink or green) |
| November | Topaz | Topaz Quartz | Topaz (citrine) |
| December | Turquoise | Zircon | Zircon |