Your Birthstone According to the Middle Ages

By Cait Stevenson

The Canterbury Tales’ Prioress, more concerned with luxury than fighting luxuria, notoriously carries a set of prayer beads ending not in a cross but in a pendant reading “Love conquers all.” When Chaucer specifically mentions that its dainty beads are made of coral, it’s not an idle description—polished coral, like gems and minerals, had significant meanings and powers in the medieval geological imagination.

In the late fourteenth and fifteenth centuries, in fact, coral was undergoing a change in meaning. To high medieval scholars like Thomas of Cantimpré, the branching nature of living coral took the shape of Christ’s cross, giving it strong powers as a ward against things like storms and epilepsy. By the early modern era, coral amulets promised success in earthly, lustful love. Chaucer’s use of coral, therefore, seems to add to the devotional ambivalence of the character.


Most of us today are probably familiar with the concept of birthstones—precious gems associated with each month, like a petrological Zodiac. It turns out birthstones are more or less an invention of modern jewelry manufacturers, whose meanings all boil down to “Buy this ring.” But this is boring. So I thought, why not make birthstones mean something today by looking at their superpowers according to the Middle Ages?

Fortunately, there’s an entire genre of texts known as lapidaries, from authors like Bartholomeus Anglicus and Albert the Great, to help us out!


Aquamarine stone with the portrait of Julia Domna (died AD 217), the wife of Emperor Septimius Severus.


Aquamarine is a form of beryl, to which were attributed all sorts of fantastical powers.

…except medieval lapidary authors’ descriptions make it clear their idea of beryl was really clear rock quartz. So instead, the stone “diacodos” or substitute was lightly colored quartz or beryl, like aquamarine. It was a favorite of magicians in the Hermetic tradition—perhaps used for some crystal-gazing fortune telling, but  also supposed to help a person summon demons.

What gives, March? Your other birthstone, bloodstone, also had a much stronger presence in necromantic texts than quasi-scientific ones (and not because of its vaguely creepy modern name—it was called “heliotropium” in the Middle Ages and linked to the sun). According to ancient magicians repeated by medieval authors, a bloodstone placed in water could darken the sun or turn its light red as blood, and boil the clouds of the sky into thunderstorms.

It was also said to stop bleeding, but who needs that when you can trigger a solar eclipse on demand?



Tired of having an expensive but ubiquitous birthstone? Grab a time machine! Thanks to the tremendous hardness of diamond and skill needed to cut it properly, medieval lapidaries (the people, not the books) didn’t really bother to invest the time to master the optics of refraction to make diamond look like it does today. So writers like Thomas of Cantimpre were first of all concerned with describing ways to destroy it. For example, soaking the stone in the blood of a goat—especially a drunk goat–might soften it enough to cut it.

Diamonds could, however, protect the wearer against insanity and nightmares. Now that is how to market an engagement ring.


The green beryl we know as emerald was, in the Middle Ages, one of the recognized types of a gemstone category/variety called “smaragdus” (or the more recognizable esmaraldus). Consequently, an enormous set of abilities granted to individual varieties came to apply to the whole group. Wearing an emerald amulet could help you win arguments, get rich, cure epilepsy, prevent thunderstorms, improve your memory, and predict the future.

Medieval Emerald ring – British Museum

Well, as long as you don’t have sex. Albert the Great repeats a legend that the King of Hungary wore an emerald ring to bed. The stone was so upset even by legal and licit intercourse between the king and queen that it broke into three pieces.


Perhaps unsurprisingly, many qualities attributed to moonstone in the Middle Ages related to the moon. It was said to grown and shrink in size with the moon’s waxing and waning, and the strength of its powers skyrocketed on certain days of the lunar cycle. The moonstone was above all a tool for divination: placing it under your tongue could inculcate knowledge of a specific action one must take (or not).

…As for pearl, really the most important thing we learn is that Albert the Great really liked eating oysters, and often ended up with a mouthful of pearls for his haste in consuming them.

14th century gold ring with a ruby – The Metropolitan Museum of Art


The ruby was another gem invested with poison-neutering ability, but most of its reputation related to its deep clear red color—the color of Mars. Its monetary value to jewelers depended on how much it shown in the dark: not at all, only when water was poured over it, or all on its own “like a live coal.”


Also, congratulations—your birthstone in Greek is “anthrax.”


Sixteenth-century heraldry and arms encyclopedist Gerard Legh carefully acknowledged his debt to the medieval lapidary tradition when he noted that sardonyx could “put away lechery” and keep its bearer chaste in thought and action. But he added a military meaning onto the usual set of mystical attributes of stones. Sardonyx reminds its bearer that in battle, care is better than haste.

As a form of olivine, peridot was typically tagged as chrysolitus in medieval lapidaries. Thus, it was considered one of the twelve stones building the walls of the New Jerusalem in Revelation 21. This was of far less concern to lapidary authors—even the theologians in religious orders!—than its medical, magical, and moral powers. Marbode of Rennes said to wear peridot in a gold setting as a bracelet on your left wrist, from which it could ward off nightmares and demons. Albert the Great said he knew from observation and testing that if you ground peridot to a powder, it could cure asthma. And “expel stupidity.” Clearly, a fitting birthstone for a common “back to school” month!


Byzantine pendant showing the Virgin and Child – includes pearls, emeralds, garnets, sapphires, and a sardonyx – The Metropolitan Museum of Art

What we know today as sapphire was most probably identified as the blue form of hyacinthus or iacinthus in medieval sources. A blue “having nothing watery about it” hue was considered the most valuable form. In some accounts, sapphire was reputed as a remedy against poison—and made its wearer rich, clever, and happy.


Ancient and medieval authorities worried that staring too long at opal, trying to capture all its colors, would damage people’s eyesight. Either for that or for the similarity of its Latin name (ophthalmus) to ophthalmia the eye disease, it was associated with vision but in a deeply ambivalent way. It could protect the eyes of someone who wore it as an amulet, but damage other people’s.

Oh, yeah, and it could turn you invisible.


In the Middle Ages, topaz was thought to take the forms either of the clear orangey-yellow stone we know today, or a mockery of gold—our pyrite or fool’s gold. As the transparent topaz, it could instantaneously cool boiling water or cure hemorrhoids; as pyrite, it could scare off tornadoes.


Albert the Great describes the color and opaqueness of turquoise: “as if milk had penetrated the blue color and risen to the surface.” Turquoise was said to heal eye problems, and amulets were worn to ward off basically every kind of misfortune.

In itself, lapis lazuli was considered a strong opposition to disorders caused by excessive black bile, especially fever and fainting. (Sometimes it was considered a form of sapphire with the attendant powers…the more valuable form!)  However, lapis lazuli is the semi-precious gem whose primary special use was artistic rather than medical. It was the source of the famous (and infamously expensive) pigment ultramarine so loved by late medieval and Renaissance painters—at least, those who could afford it.


The stones medieval people recognized as garnet tended to be darker red or red-violet than rubies. Jewellers recommended setting them against black. Garnet was the happy gem! Forget poison prevention—garnet warded off sorrow and brought gladness.


Amethyst was said to prevent drunkenness.

Somehow this never shows up in sermons against gluttony.

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