Birthstones by month, their colours and why

A vote in Kansas City

In August 1912, at a meeting in Kansas City, the American National Retail Jewelers Association approved a new list of birthstones. One stone for each month, with a few alternatives, set down in a table that anyone could follow.

Not everyone was charmed. The gem expert George Frederick Kunz, writing the following year, said the new list could "scarcely be said to offer a satisfactory solution". He was particularly cross that ruby had been moved to July and turquoise to December. The idea was that a warm red suited summer and a pale blue suited winter. Kunz thought it was exactly the wrong way round: in winter, he pointed out, we want warmth.

More than a century later, the list he grumbled about is still the backbone of every birthstone chart. Here it is, as it stands today.

The stones, month by month

This is the modern list as published by Jewelers of America, the trade body that the 1912 association became.

A few of those colours come with a footnote. Ruby and sapphire are the same mineral, corundum: ruby is the red variety, and sapphire is usually blue but can be almost any other colour. Most blue topaz on sale today was colourless topaz that has been treated to turn it blue, a permanent change. And most citrine is amethyst that has been heated.

Ancient roots

The story starts with the breastplate of the high priest Aaron, described in the Book of Exodus, which was set with twelve stones for the twelve tribes of Israel. In the first century, the historian Josephus linked those twelve stones to the twelve months and the twelve signs of the zodiac. In the early fifth century, St Jerome took up the same idea.

Identifying the original stones is harder than it sounds. Ancient gem names described colour more than mineral, and many have shifted meaning since. Kunz noted, for example, that the stone translated as "sapphire" in the old lists was almost certainly lapis lazuli.

Wearing the stone of your own birth month came much later. Kunz traced the custom to Poland in the eighteenth century, though he was careful to say only that this is where it appears to have begun.

The 1912 list

By the early twentieth century there were several competing lists, all loosely based on the breastplate or on the twelve foundation stones of the New Jerusalem in the Book of Revelation. The jewellers who met in Kansas City in 1912 settled on this.

Compare it with today's list and the bones are the same. Two months have quietly swapped their leading stones: aquamarine has overtaken bloodstone in March, and peridot has overtaken sardonyx in August. Bloodstone, a dark green stone with red spots, still has its supporters, and some lists keep it for March.

What has changed since

The American list has been formally updated three times since 1912.

• 1952. Alexandrite was added for June, citrine for November, tourmaline for October and zircon for December.
• 2002. On 30 October 2002, the American Gem Trade Association added tanzanite to December, alongside turquoise and zircon. It was a young gem to be given such an honour: its main source, in Tanzania, was only located in 1967.
• 2016. In June 2016, Jewelers of America and the American Gem Trade Association jointly added spinel to August, alongside peridot. Spinel had spent centuries being mistaken for ruby, and was not clearly separated from it by chemistry until the eighteenth century.

Each change gave a month a new colour to choose from. December now runs from the sky blue of turquoise to the violet of tanzanite, and August from peridot's lime to spinel's reds and pinks.

The British list

Britain went its own way. In 1937 the National Association of Goldsmiths drew up a standard British list, which offered alternative stones for months whose main stone might be hard to find or to afford.

In 2015 the National Association of Goldsmiths and the British Jewellers' Association voted to merge, forming the National Association of Jewellers. Its list today gives a traditional stone and an alternative for every month.

Where the US and UK lists differ

For most months the two lists agree on the main stone. The differences are in December, and in the extra stones.

• December is the real split. The British list leads with tanzanite and offers blue topaz. The American list names turquoise, tanzanite and blue zircon.
• Alexandrite appears for June on the American list but not on the British one.
• The British alternatives bring in stones the American list doesn't use at all: rose quartz, amber, jade, rock crystal, chrysoprase, carnelian, lapis lazuli and blue topaz.
• Bloodstone survives for March on some American lists, including those of the American Gem Trade Association and GIA, but not on Jewelers of America's or the British list.

Why these colours?

Colour has always been the thread. The ancient lists were really lists of colours, since the names meant colours more than minerals. That is why the same month can carry a costly gem and a modest one of a similar shade.

Price and availability matter too. GIA, the Gemological Institute of America, puts the extra stones in some months down mainly to rarity and cost: some gems are rarer and more expensive, and others are simply less popular. The British list says so openly, presenting its alternatives for anyone who would like a choice.

And then there is the seasonal argument that so annoyed Kunz: warm reds for summer, cool blues for winter. Whatever you make of it, it is the reason ruby sits in July.

Lab-grown and look-alike birthstones

Many birthstones are also made in laboratories. Ruby was the first: Auguste Verneuil announced his flame-fusion method for making it in 1902. Laboratory-grown sapphire, emerald, spinel, alexandrite and amethyst are all made today, and they share virtually all the properties of the natural gems.

That is why the rules are strict about naming. In the United States, the Federal Trade Commission's Jewelry Guides say the word "birthstone", like the name of the gem itself, must be qualified with a word such as "laboratory-grown", "laboratory-created", "imitation" or "simulated" when the stone wasn't mined. A laboratory-grown ruby is real ruby, made by people; a red glass imitation is not ruby at all. Our guide to cubic zirconia, lab-grown and natural stones explains the difference in full.

A list that keeps growing

Kunz worried that the 1912 list was a commercial convenience dressed up as tradition, and that people would lose interest in birthstones if they felt sentiment was being exploited. He was half right. The list has been changed, more than once, for practical reasons. But the feeling behind it has never really gone away. A stone the colour of your month, chosen for you, still says what it said in Kansas City: this one is yours.