Birthstones, month by month and sign by sign

Four lists, none of them authoritative

Ask what your birthstone is and you will get a different answer depending on who you ask, because at least four separate traditions are in circulation and they were built for different purposes.

The modern month list is the one printed on jewellery-shop cards. It was standardised by the American National Association of Jewelers in 1912, revised in 1952, and amended twice since: tanzanite joined December in 2002 and spinel joined August in 2016. It is a commercial standard, drawn up so that shops in different states would stock the same thing, and it works well for exactly that. It is not old and it does not claim to be.

The traditional lists are what the modern one replaced, and they vary by country and century. Polish, Russian, Italian, Hebrew and Arabic lists all differ. Many of them descend from attempts to match the twelve stones of Aaron's breastplate in Exodus 28 to the twelve months, a matching first proposed by Josephus in the first century and by Saint Jerome in the fifth, and complicated by the fact that nobody now knows for certain which minerals the Hebrew names refer to.

The Ayurvedic navaratna is not a birthstone system at all in the Western sense. Nine gems answer to nine planets, and which one you should wear depends on your birth chart rather than on your birth month, with the strength and placement of the relevant planet deciding whether a stone is prescribed at all. A Jyotish astrologer may well tell you not to wear the stone your Western list assigns.

A fifth set circulates as the mystical or Tibetan list, and it is worth naming because it is widely reproduced: garnet for January, amethyst for February, jade for March, opal for April, sapphire for May, moonstone for June, ruby for July, diamond for August, agate for September, jasper for October, pearl for November and onyx for December. No verified Tibetan source for it has ever been produced, it appears in English-language literature of the twentieth century, and it is best treated as a modern list with an attributed pedigree rather than an old one.

The zodiac lists sit between the two. They are widely reproduced, rarely sourced, and disagree with each other more than any other set. This library gives the most commonly cited assignment for each sign, states which planet rules it, and says where the assignment is contested.

How Jyotish actually decides

The Vedic system is the only one of the four that claims to be doing something consequential, so it is worth setting out how it works rather than just naming its nine gems.

The practice is called ratna upaya, gemstone remedy, and it rests on one premise: a gem amplifies the planet it belongs to. It does not soothe that planet, balance it or negotiate with it. It turns it up.

Everything else follows from that. Because a gem amplifies, you only wear the stone of a planet that is favourable to you but weak in your chart, so that something already working in your favour gets strengthened. This principle is anukul-vad, and it is the mainstream of the tradition.

The opposite belief, that wearing a gem will pacify a troublesome planet, is called pratikul-vad, and Jyotish rejects it firmly. On the tradition's own logic, wearing the stone of a planet that is causing you difficulty will amplify the difficulty. This is the single most common misunderstanding in Western repackagings of the system, and it inverts the actual instruction.

Which planets are favourable is decided by the lagna, the ascendant, meaning the sign rising on the eastern horizon at the moment and place of birth. The lagna changes roughly every two hours, so two people born on the same day in the same city can be given opposite advice. That is precisely why no birth-month table and no sun-sign chart can substitute for the reading, and why a Jyotish astrologer may tell you to wear nothing at all.

The nine gems are ruby for the Sun, pearl for the Moon, red coral for Mars, emerald for Mercury, yellow sapphire for Jupiter, diamond for Venus, blue sapphire for Saturn, hessonite for Rahu and cat's eye chrysoberyl for Ketu. Blue sapphire carries the strongest cautions and is traditionally tested for a short period before it is committed to.

How to use a birthstone list without being sold to

Treat the month list as what it is, a pleasant shared convention with a clear commercial origin, and enjoy it on those terms. Treat the traditional lists as history, and read them for what they reveal about the period that made them. If you want a stone chosen for you personally rather than by your birth month, the Ayurvedic system is the only one of the four that was built to do that, and it requires an actual chart reading rather than a chart-free lookup table.

And know the escape hatch: none of the lists obliges you. A stone you chose because it means something to you will outperform a stone assigned to you by a committee in 1912, on every measure that matters to a practice.