The Birthstone Handbook

A grandmother comes in with a date in her head and a granddaughter turning eighteen. She knows the month. She has been told the stone. She would like, please, a sapphire, because the girl was born in September, and that is simply how it works. She has the loveliest expression while she says it — the expression of somebody handing over something that was decided long before either of us was born.

I love that conversation, and within four minutes I am going to complicate it, because the honest answers to her next three questions are: the list was standardised by a retailers’ association in 1912; on trade estimates, roughly nine in ten commercial sapphires have been through a furnace; and the price she has in mind is either far too low or unnecessarily high, depending on which of those facts she cares about more.

None of that spoils the gift. It is the gift. A stone chosen with the facts in hand is a better present than a stone chosen from a poster, and it tends to survive contact with the granddaughter’s actual life — her gym bag, her washing up, her habit of putting rings in her pocket.

Why this volume exists

Birthstones are the single most common way people in Australia meet coloured gemstones. They are the reason a great many first pieces get bought, and they are also the reason a great many disappointing pieces get bought: a stone assigned by calendar rather than by suitability, mounted in the wrong setting, treated in a way nobody mentioned, and cleaned six months later in a way that quietly ruins it.

The guides currently available online are, in the main, accurate about the twelve names and thin about everything else. They will tell you October is opal and tourmaline. Very few tell you that opal sits at 5 to 6.5 on the Mohs scale and can craze under a sudden temperature change, that much cheap opal jewellery is a doublet or triplet that dislikes prolonged water, or that the vast majority of blue topaz sold anywhere has been irradiated and heated. Those are not trade secrets — they are on GIA’s public month pages. They are simply not what a chart is designed to say.

What I have tried to do differently

This handbook does four things that a chart cannot. It dates the history properly, including the parts that are contested and the parts that are frankly commerce. It tells you, month by month, what is normally done to each stone before it reaches a display case, and what the disclosure rules actually require. It translates hardness and toughness into the only question that matters at the counter — ring, pendant, or occasional wear. And it gives you honest price ranges, with a clear note on where those ranges come from and how much confidence they deserve.

Where the authorities disagree, I say so rather than picking whichever version reads more romantically. There are at least a dozen points in this subject where the trade repeats something with total confidence and no primary source underneath it, and I flag each as I reach it. To our knowledge no other consumer birthstone guide sets the American and British lists side by side and tells you which one you are unknowingly using.

Where I am standing

You should know my position before you weigh my advice. I am an FGAA-qualified gemmologist. I assess every stone that passes through this house, and I write the treatment line on every one of them. We sell only natural, earth-mined gems. That is a house preference, not a verdict on anybody else: laboratory-grown stones are a legitimate product, honestly made, and a lab-grown alexandrite disclosed as lab-grown is a perfectly good thing to buy. What is not legitimate — ever, in either direction — is silence about which one you are holding.

The same goes for treatment. Heat, oil, irradiation and impregnation are all long-standing, accepted practices. Some of them make a stone possible at a price a normal person can pay. A heated aquamarine is not a lesser thing; it is simply an aquamarine that has had the green removed, as nearly all of them have. The sin is never the treatment. The sin is not being told.

So read this as a letter from someone who spends her days under a microscope and would rather you bought the right stone than the flattering one. Skip to your own month if you like.

— Anna, FGAA
Ministry of Gems, Sydney

There are two stories about birthstones and they are both true, which is why the subject confuses people. The first story is very old and concerns twelve stones, twelve tribes and twelve signs. The second is a little over a century old and concerns a trade association that wanted its members to stop arguing about what to put in the window in March. The modern list is the second story wearing the first story’s clothes.

Aaron’s breastplate and the first twelve

The oldest root anybody can point to is the breastplate of Aaron, described in the Book of Exodus and set with twelve stones representing the twelve tribes of Israel. That is the origin the International Gem Society and the trade press both give, and it is where every serious history of the subject begins.

The leap from twelve tribes to twelve months came later. In the first century CE the historian Flavius Josephus connected the breastplate stones to the twelve months of the year and the twelve signs of the zodiac — the move that, in the histories that survive, first mapped stones onto time rather than onto lineage. In the fifth century St Jerome encouraged Christians to make use of the breastplate stones, which gave the idea a long institutional life. By the eighth and ninth centuries a devout and wealthy person’s practice was to own all twelve stones and wear the appropriate one each month, rotating through the year.

Read that again, because it undoes the whole premise of the modern gift. For most of the tradition’s history you did not have a birthstone. You had twelve of them, and you wore whichever one the calendar was currently on.

When did we start wearing only our own?

Here the record goes soft, and anyone who tells you otherwise is guessing confidently. The International Gem Society places the shift — from owning all twelve to wearing only your own birth month’s stone — in sixteenth-century Germany or Poland. George Frederick Kunz, writing in 1913, attributed it instead to eighteenth-century Poland, and to his considerable credit hedged the claim himself: it seemed to him highly probable, which is not the same as documented.

Two centuries apart, two respectable sources, and no primary documentation that settles it. I have looked. This is the first of several places in this subject where the honest answer is that we do not know, and where I would rather say so than pick the tidier date. If a chart gives you a single confident century for the birth of the custom, it is repeating one of these two guesses without telling you it is a guess.

1870: the poem nobody signed

In 1870 Tiffany & Co. published a pamphlet containing twelve four-line birthstone poems — the “Gregorian” verses — assigning one lucky stone to each month. The verses have been quoted ever since as though they were folk tradition handed down through generations.

The pamphlet was anonymous, and there is no record of the verses existing before that publication. They are, on the available evidence, marketing copy: charming, effective, and about as ancient as the sewing machine. I have no objection to them at all — I rather like them — but if a seller quotes you the poem as proof of antiquity, you now know the publication date and can enjoy it for what it is.

Kunz himself is a genuinely important figure here rather than a villain. Tiffany & Co.’s gemmologist, born 1856 and died 1932, he wrote the firm’s “Natal Stones” pamphlet and then, in 1913, “The Curious Lore of Precious Stones” — the first comprehensive scholarly treatment of gem lore, birthstones included. Nearly everything written about birthstone history since draws on him. That he worked for a jeweller does not make his scholarship worthless; it does mean the discipline’s founding text was written from inside the trade.

Kansas City, August 1912 — and the three amendments since

The list you will be handed in an Australian shop today descends from a decision made in August 1912, when the American National Retail Jewelers Association — now Jewelers of America — adopted the first standardised birthstone list at its convention in Kansas City. The purpose was explicit and commercial: regional and historical lists contradicted one another, which made stocking and selling a mess, so the trade standardised its terminology. The 1912 list also, as several histories note, quietly favoured transparent gems over opaque ones, which is exactly the preference you would expect from people who had faceted stock to move.

Three amendments have followed, and each is precisely dated:

1952. The Jewelry Industry Council of America updated the list, adding alexandrite for June, citrine for November, pink tourmaline for October, and zircon for December in place of lapis lazuli, with adjustments to March’s primary and alternate stones. Fair warning: the 1952 details are the muddiest part of this history. Sources agree on the four additions but differ on the March changes and frequently misattribute the amending body to the retail jewellers’ association. Primary 1952 documentation is almost never cited by anyone, including the people quoting it.

2002. On 30 October 2002 AGTA announced that tanzanite had been added as a December birthstone — the first change in half a century — through an industry consensus that included GIA and the International Colored Stone Association. A stone discovered in the 1960s joined a list rooted in Exodus, which tells you something useful about how living the list is.

2016. On 2 June 2016 Jewelers of America and AGTA jointly announced spinel as an official August birthstone alongside peridot, with the consumer launch that July. AGTA’s chief executive Doug Hucker made the nice historical point at the time that ancient merchants knew red spinel as “balas ruby” and that spinel was only separated from ruby chemically in the late eighteenth century. In other words, spinel was not a new stone joining an old list. It was an old stone finally being called by its own name.

So the honest summary is this: the twelve-stone idea is genuinely ancient, the one-stone-per-person custom is somewhere between 250 and 550 years old depending on which of the two authorities you follow and is undocumented either way, and the specific list on the poster is a twentieth-century retail convention that has been amended three times, most recently within the last decade.

Australians sit oddly on this subject. We inherited British jewellery conventions and we consume American jewellery marketing, and the two do not agree about March or December. Nobody points this out at the counter, because nobody at the counter knows.

The modern list, as GIA and the American Gem Society publish it

The current American list, on which GIA and the American Gem Society agree, runs: January garnet; February amethyst; March aquamarine and bloodstone; April diamond; May emerald; June pearl, alexandrite and moonstone; July ruby; August peridot, spinel and sardonyx; September sapphire; October opal and tourmaline; November topaz and citrine; December tanzanite, turquoise and zircon.

Three months carry three stones each — June, August and December — and only those three. That is not a rounding error in the chart you are reading; it is the actual state of the list. Jewelers of America, the institutional descendant of the 1912 association, acts as steward of it, and jointly announced the most recent change with AGTA in 2016.

The British list of 1937, which nobody mentions

Britain has its own standardised list. The National Association of Goldsmiths published it in 1937, twenty-five years after the American one, with main stones and alternatives of its own. It has never been harmonised with the American list and it still differs in ways that matter to a buyer.

Bloodstone is far more prominent for March in the British scheme, where the American list treats it as the traditional companion to aquamarine. December keeps turquoise and does not include tanzanite, for the excellent reason that tanzanite had not been discovered in 1937 and Britain never adopted the 2002 amendment. And there is no August spinel, because that change happened in 2016 in the United States.

This is worth knowing because a great deal of British and Commonwealth family jewellery follows the older logic. If your grandmother’s December brooch is turquoise rather than tanzanite, she was not confused. She was using a different list.

December: three stones, or four?

Here is a genuine category error in circulation. GIA and the American Gem Society list three December stones: tanzanite, turquoise and zircon. A number of large retailers publish four, adding blue topaz.

Blue topaz has never been added to the official list by Jewelers of America or AGTA. There has been no fourth amendment. Its December status is retail custom — a stone that is inexpensive, reliably blue, available in every size, and therefore extremely convenient to sell in December. I am not going to pretend that is a scandal, and blue topaz is a pleasant stone. But if you have been told blue topaz is “an official December birthstone”, it is not, and the person telling you may not know that.

The same instinct runs the other way in August, where a good many modern retail guides silently drop sardonyx and present a two-stone month. Sardonyx is the original August stone with more than four thousand years of history behind it. Keeping it is both more accurate and considerably more interesting than dropping it.

Zodiac stones, anniversary stones, and other systems

People arrive assuming zodiac stones are a parallel official list. They are not a list at all. No authority publishes one, and vendor charts openly contradict each other — Leo appears as onyx in one and peridot in another, Taurus as emerald in one and sapphire in the next. Zodiac assignments also follow sun-sign date ranges rather than calendar months, so they straddle two birthstone months and produce two different correct answers for the same person. Choose one if you enjoy it; do not pay a premium for authenticity that does not exist.

Anniversary stones, by contrast, are reasonably consistent. The chart recognised across Jewelers of America, the American Gem Society, AGTA and GIA gives ruby at forty years, sapphire at forty-five, alexandrite at fifty-five and diamond at sixty. GIA’s month pages confirm a longer sequence: garnet at two, tourmaline at eight, turquoise at eleven, citrine at thirteen, opal at fourteen, peridot at sixteen, aquamarine at nineteen, emerald at twenty and thirty-five, spinel at twenty-two, tanzanite at twenty-four, and diamond at sixty and seventy-five. If your birth month has landed you with a fragile stone, an anniversary year is a graceful way to justify a different one.

And it is worth remembering that the month system is not universal. In Hindu Vedic tradition, stones are assigned by planets rather than months, and zircon alternates with hessonite garnet among the nine navaratna gems. There is no global standard anywhere: CIBJO, the world jewellery confederation, publishes no birthstone standard at all. What you are choosing between is conventions, and it is entirely legitimate to choose the stone you actually like.

What follows is the working version of the chart. For each month: the honest identity of the stone, the treatment norm, the durability verdict, and the trap.

January and February: the untreated one, and the one with a synthetics problem

January — garnet. The first thing to understand is that garnet is not a stone, it is a mineral group. Five species matter as gems — pyrope, almandine, spessartine, grossular and andradite — and between them they cover far more than the dark red everybody pictures. Tsavorite is a green grossular garnet. Spessartine runs a vivid mandarin orange. If someone has told you their garnet is green, they are not confused.

Hardness runs 6.5 to 7.5 across the group, which makes garnet comfortable in earrings and pendants and workable in a ring with a little care. Its real distinction is honesty: most garnets are not treated at all. Fracture filling exists but is rare, and such stones do need special care. That makes garnet one of the genuine value propositions on the list — an untreated natural gem, in a range of colours, at a sane price. GIA also notes on its January page the fact that anchors this whole subject: artisanal, small-scale miners are estimated to supply some 80 per cent of the world’s gems. Garnet is a two-year anniversary stone.

February — amethyst. Heat is the common enhancement, used to lighten over-dark material, and it can convert some amethyst to citrine — hold that thought until November. The colour change is permanent, but be aware that some amethyst fades under prolonged strong light, which is an argument against leaving a favourite piece on a sunny windowsill in a Sydney summer. At 7 on the Mohs scale it is perfectly suitable for a ring worn daily, with an occasional repolish over the years.

The February trap is synthetics. Laboratory-created amethyst has been in the market since the 1970s and is very difficult to separate from natural material without advanced testing — difficult enough that testing every inexpensive stone would cost more than the stone. Sellers are required to disclose synthetic origin, and a straightforward seller will simply tell you. If a purple stone is remarkably cheap and nobody will say the word “natural” in writing, you have your answer.

March and April: durable, and quietly treated

March — aquamarine, with bloodstone. Nearly all aquamarine on the market has been heated to roughly 370 to 425°C (700 to 800°F) in a reducing atmosphere, to drive off the green and settle a stable blue. The result is permanent and, importantly, undetectable — which is why laboratories treat it as universal practice and generally decline to comment on it at all. This is the clearest example on the whole list of a treatment so standard that it has stopped being news. It should still be said out loud, and I say it.

At 7.5 to 8 Mohs aquamarine is genuinely durable for everyday wear, which puts it in a small club among the softer coloured stones. It also produces spectacular crystals: Eleanor Roosevelt was given a 1,298 ct Brazilian aquamarine in 1936, and the Dom Pedro weighs 10,363 ct. Bloodstone, the traditional and distinctly British March alternative, is a dark green chalcedony flecked with red, at 6.5 to 7. Aquamarine is the nineteenth anniversary stone.

April — diamond. At 10 on the Mohs scale, diamond is the hardest gemstone and the most forgiving thing you can put on a hand. The largest rough diamond ever found remains the 3,106 ct Cullinan, recovered in 1905. The one caveat worth carrying: treated diamonds and heavily included ones need gentler cleaning than untreated stones, because a fracture-filled or heavily included stone is not the invulnerable object the marketing implies. Diamond marks the sixtieth and seventy-fifth anniversaries.

May: the stone you must never put in an ultrasonic

May — emerald. Emerald is routinely clarity-enhanced. Oils, waxes and artificial resins are used to fill surface-reaching fractures, in amounts that range from minor to significant, with stability that varies by material. Paler material is also sometimes dyed. This is not a fringe practice; it is the norm, and a laboratory report on a fine emerald will grade the degree of enhancement as a matter of course.

The practical consequences are severe and I want them in plain language. Never put an emerald in an ultrasonic cleaner. Never steam-clean one. Even hot dishwater can damage a filled stone by drawing out the filler and leaving the fractures suddenly visible. Emerald is 7.5 to 8 on the Mohs scale — hard enough on paper — but brittle in practice because of those fissures. It is a stone I am happy to set in a ring for someone who understands what they have, and reluctant to set for someone who wants to garden in it.

Colombia has been the benchmark source for more than five hundred years, through Muzo, Chivor and Coscuez, with Zambia, Brazil, Afghanistan and Pakistan the other major producers. Emerald marks the twentieth and thirty-fifth anniversaries.

June: three stones, three entirely different problems

Pearl. Cultured pearls account for the vast majority of pearl sales today, because natural pearl beds were decimated by millennia of fishing. At 2.5 to 3 on the Mohs scale, pearls are the most delicate mainstream gem by a wide margin: store them separately, put cosmetics and perfume on before the pearls, wipe them after wear. The June trap is that akoya pearls are routinely bleached with hydrogen peroxide and pinked with dye absorbed through the drill hole — so universal the trade treats it as standard processing. The disclosure rules apply to pearls exactly as to stones.

Alexandrite. Colour-change chrysoberyl, discovered in Russia’s Ural Mountains in 1830 and named for the future Tsar Alexander II. The Ural deposits are mined out; supply now comes from Brazil, Sri Lanka and East Africa, generally with a less precise colour change than the Russian legend. GIA describes fine-quality alexandrite as one of the more expensive coloured gems, specifically because of its scarcity in larger sizes. At 8.5 Mohs with excellent toughness it is genuinely suited to a daily ring. The trap: most alexandrite in mass-market jewellery is laboratory-created — a legitimate product, honestly sold, and a poor thing to pay natural prices for. Alexandrite is the fifty-fifth anniversary stone.

Moonstone. The finest material shows a blue adularescence — that floating internal glow — across a colourless body. India and Sri Lanka are the important sources, and Ceylon is the classic one. At 6 to 6.5 with poor toughness, moonstone is a pendant and earring stone. It is not a daily ring, whatever the photographs on social media suggest, and I have re-cut enough chipped ones to be firm about it.

The back half of the year holds the two hardest coloured stones anybody sells and four of the most treatment-heavy gems on the chart. Read your own month, then read November regardless.

July and August: the durable month, and the one that isn’t

July — ruby. Rubies are routinely heated, to drive off purplish tones and dissolve the fine rutile inclusions the trade calls silk. The trade accepts heat without argument because it is stable and permanent. Lower grades are another matter entirely: they may be lead-glass filled or dyed, and a glass-filled ruby can be damaged by something as ordinary as lemon juice. Such a stone should only ever be wiped with a damp cloth — no ultrasonic, no steam, no acidic cleaner.

GIA is unambiguous that treatments affecting value must be disclosed under the FTC’s rules, and its advice to buyers is the question I would like you to memorise: is this stone treated, and by what method? Ask for the answer in writing. At 9 on the Mohs scale, corundum — ruby and sapphire are the same mineral — is an excellent daily-wear stone. Myanmar’s Mogok has been the classic source for over five hundred years, alongside Vietnam and, as the major modern producer, Mozambique’s Montepuez; Sri Lanka is among the historic producers. Ruby marks the fortieth anniversary.

August — peridot, spinel and sardonyx. This month shows why the list needs reading rather than obeying. Peridot, the long-standing primary, sits at 6.5 to 7 and, in GIA’s own assessment, cannot take hard wear and is not recommended for daily use in a ring. It is vulnerable to acids — including, over the long term, acidic perspiration — and must never see an ultrasonic or a steamer. A beautiful stone in earrings; a slow disappointment on a working hand. Peridot is the sixteenth anniversary stone.

Spinel, added in 2016, is the modern star and my own quiet favourite. It is 8 on the Mohs scale, thoroughly durable in a ring, and — the part that matters most — very rarely treated. GIA lists only occasional heat or fracture filling; untreated is simply the norm. It also has the best story on the list: the roughly 170 ct red stone known as the Black Prince’s Ruby, sitting in Britain’s Imperial State Crown above the 317.40 ct Cullinan II, is not a ruby at all. It is spinel, received by Edward the Black Prince in 1367, and nobody could have known otherwise, because spinel was only distinguished from ruby chemically in the eighteenth century. Sri Lanka’s Ratnapura district has produced it for centuries. Spinel is the twenty-second anniversary stone.

Sardonyx, the original August stone with more than four thousand years of history, is a banded chalcedony at 6.5 to 7 and is commonly dyed. That is worth knowing before you pay for “natural colour” banding.

September: the benchmark, and its two dangerous treatments

September — sapphire. The stone I know best, and the one I am most careful about. Heat treatment is common and permanent, which is why the trade accepts it; a heated sapphire is a real sapphire and there is nothing wrong with owning one, provided you paid a heated price.

The uncommon treatments are where the danger lives. Lattice diffusion can produce colour so shallow that it is lost entirely if the stone is re-cut or chipped — you can lose the blue in a repair. Fracture-filled and dyed sapphires are damaged by mild acids, lemon juice included. None of these are hypothetical. Ask before buying, and get it in writing.

Trade estimates put 90 to 95 per cent of commercial sapphires as heated, with unheated stones commanding premiums of roughly 30 to 50 per cent, rising to 200 to 300 per cent for fine stones above five carats. I want to be scrupulous here: those are trade estimates, widely repeated and not laboratory-audited. GIA itself says only that heat is common. Treat the percentages as the shape of the market rather than a measurement.

At 9 Mohs with excellent toughness, sapphire is the benchmark daily-wear coloured stone, which is why it has become the default alternative for engagement rings. Sri Lanka has produced sapphire for more than two thousand years, and it was Ceylon’s milky geuda material, heated to rich blue, that triggered the treatment revolution which reshaped the market. Kashmir’s legendary cornflower stones came from a deposit found after an 1881 landslide and mined mainly between 1882 and 1887 — six years that still set the price of a word on a report. Australia and Montana are among the other significant sources GIA names. Sapphire marks the forty-fifth anniversary.

October and November: Australia’s month, and the most treated stone in the shop

October — opal and tourmaline. Opal is Australia’s month in every meaningful sense. Our fields are the world’s most productive: Lightning Ridge in New South Wales for black opal, White Cliffs and South Australia’s Coober Pedy, Andamooka and Mintabie for white. Boulder opal comes from exactly one place on Earth, and that place is Queensland.

Opal is also the most misunderstood stone on the list. At 5 to 6.5 Mohs it can fracture under heat or a sudden temperature change — a hot car, a sink of hot water. Treatments include oil, wax and plastic impregnation. And a great deal of inexpensive opal jewellery is not solid opal but a doublet or triplet: a thin slice glued to a dark backing, sometimes capped with a quartz dome, which prolonged water exposure can weaken. Store opal away from harder gems, and take it off before the washing up. Opal is the fourteenth anniversary stone.

While we are here: the idea that opal is unlucky is a literary artefact, traceable to Sir Walter Scott’s 1829 novel “Anne of Geierstein”. There is no significant European tradition of unlucky opal before it — the Romans called opal the queen of gems. The frequently repeated claim that European opal sales halved after publication has no primary source I can find, so I pass it on as lore about lore.

Tourmaline is the more practical October option at 7 to 7.5, generally fine for everyday wear, though heat is damaging and it should never go near an ultrasonic or steamer. Copper-bearing Paraíba tourmaline, found in Brazil in the late 1980s and later in Mozambique and Nigeria in the early 2000s, far outprices every other tourmaline — if a vivid neon blue-green stone is being offered cheaply as Paraíba, something is wrong. Tourmaline is the eighth anniversary stone.

November — topaz and citrine. November is the month that shows how much quiet processing sits behind ordinary jewellery. GIA’s position on blue topaz is blunt: the vast majority seen today is the permanent result of treating colourless topaz with irradiation and heating. Not some — the vast majority. Mystic topaz, with its oil-slick rainbow, is a thin artificial coating that abrasives will remove.

The irradiation is regulated rather than sinister. In the United States the Nuclear Regulatory Commission oversees the initial distribution of irradiated gems — blue topaz by far the most common — and requires stones to be held until residual radioactivity decays to safe levels. As of 2007 irradiated topaz was estimated at around 8 per cent of the US coloured-stone business at wholesale, which gives you the volume involved. Topaz is 8 on the Mohs scale but has poor toughness because it cleaves: protect it from knocks, and keep it away from steam and ultrasonics.

Citrine tells the same story from the other end. Most citrine in the marketplace is heat-treated amethyst — which is why February and November are, chemically, often the same stone at different temperatures. Genuinely natural unheated citrine is scarce; Bolivia’s Anahí mine is a noted natural source. At 7 Mohs with good toughness, citrine is one of the soundest budget stones for daily wear on the whole list. It is the thirteenth anniversary stone.

December: three blues, one of them from a single hill

Tanzanite. Blue zoisite was identified in 1962; the primary Merelani Hills deposit was located in 1967; the stone was named for Tanzania and launched by Tiffany & Co.’s 1968 advertising campaign. The Merelani Hills remain the only commercial source on Earth, which is remarkable enough without embellishment. You will often see tanzanite called a thousand times rarer than diamond; that figure has no peer-reviewed basis and I would leave it alone. Single-source supply and a finite mine life are the defensible facts.

Most tanzanite begins as brownish zoisite and is heat-treated to its permanent blue-violet. The treatment is near-universal and creates no additional durability concerns — but at 6 to 7 Mohs tanzanite abrades easily, and GIA recommends it for earrings and pendants rather than daily wear in a ring. I agree, and I say so to every December buyer who arrives wanting an engagement ring. Tanzanite is the twenty-fourth anniversary stone.

Turquoise at 5 to 6 is commonly dyed or impregnated with epoxy or acrylic resin to improve hardness and colour, with cavities sometimes filled with metal-loaded epoxy to imitate pyrite matrix. It is damaged by acids, cosmetics and even skin oils, and must never see steam or an ultrasonic. Hubei in China is now the world’s largest producer; Iran’s Nishapur is the thousand-year classic. Turquoise is the eleventh anniversary stone.

Zircon — a real mineral, not to be confused with cubic zirconia — is commonly heat-treated to produce blue and colourless stones, along with orange, yellow and red. One quirk worth knowing: some heated zircons drift back toward brown under prolonged bright light. At 6 to 7.5 it abrades rather than shatters, so avoid rough wear. Sri Lanka’s Elahera and Australia’s Harts Range are both named by GIA as sources, giving zircon a foot in each of this house’s two countries.

If you take one chapter from this handbook, take this one. The month is decoration; what was done to the stone is the actual transaction, and the largest determinant of a fair price. Treatment is legitimate when it is disclosed and priced accordingly — the offence is never the furnace, it is the silence.

The rule, and its three triggers

The clearest written standard in the industry is the FTC Jewelry Guides, revised in July 2018 and codified at 16 CFR Part 23. Under them it is deceptive to fail to disclose a gemstone treatment when the treatment meets any one of three triggers: it is not permanent; it creates special care requirements; or it significantly affects the stone’s value. Disclosure must be clear, conspicuous, and made before the point of sale — not on a receipt afterwards. The same rules apply to pearls and cultured pearls as to faceted stones.

Those are American rules, quoted because they are the most explicit and because they shape what global suppliers write on their paperwork. Australian consumers have their own footing: under the Australian Consumer Law, goods sold to a consumer come with guarantees, among them that the goods match their description. A stone described simply as sapphire when it has been lattice-diffused, or as ruby when it is a lead-glass composite, is a description problem before it is an ethics problem. That is a consumer-purchase protection, it works differently between businesses, and it is not legal advice from me.

Notice what those triggers do not cover. A treatment that is permanent, creates no special care requirement and does not move the price need not be disclosed. Laboratories decline to comment on heated aquamarine for a related but separate reason: the treatment is permanent and undetectable, so there is nothing for a report to say. We write it down anyway.

The treatments almost nobody mentions

Assembled from the month chapters, here is the honest census of what is routine:

Near-universal, permanent, rarely discussed: aquamarine is nearly always heated to remove green. The vast majority of blue topaz is irradiated and heated. Most citrine on the market is heat-treated amethyst. Most tanzanite is heated from brownish zoisite. Akoya pearls are routinely bleached and pinked. In every one of these cases the treatment is stable and the stone is genuine; in every one of them the market price already assumes the treatment. You are not being robbed. You are simply being left uninformed, and the two feel identical when you find out later.

Common, and consequential for care: emerald is filled with oil, wax or resin, in degrees a laboratory will grade. Turquoise is dyed or resin-impregnated. Opal may be impregnated with oil, wax or plastic, and a great deal of cheap opal jewellery is a doublet or triplet rather than a solid stone. Ruby and sapphire are usually heated — harmless — but at the lower end may be lead-glass filled, dyed, or lattice-diffused, all of which change how the piece must be cleaned and repaired for the rest of its life.

The ones that will cost you money: a lead-glass-filled ruby and a fine heated ruby are not adjacent products; they belong to different price universes. A lattice-diffused sapphire can lose its colour in a re-cut. Mystic topaz is a coating that abrasives remove. None of these are illegitimate to sell. All of them are catastrophic to buy unknowingly.

The stones with clean hands

Two entries on the list stand out for having very little done to them, and both deserve more attention than they get.

Garnet is mostly untreated. Fracture filling exists but is rare. For a buyer who wants a natural stone in a natural colour with no processing history to worry about, January is a quietly excellent month across a genuinely wide colour range.

Spinel is the stronger answer still: very rarely treated, with GIA listing only occasional heat or fracture filling, and durable enough for a ring at 8 Mohs. When someone tells me they want a coloured stone with nothing done to it and do not want to pay unheated-sapphire prices, spinel is where I take them. It is not a compromise. It is the better-informed choice.

Natural, laboratory-grown, and the sentence to ask for

Treatment and origin are two different questions and get muddled constantly. A treated stone came out of the ground. A laboratory-grown stone did not.

Merchants are required to tell you which you are holding, and GIA notes this explicitly for amethyst, where synthetics have been widespread since the 1970s and are very hard to separate without advanced testing — hard enough that testing every inexpensive stone would cost more than the stone is worth. The same applies to alexandrite, where most of what appears in mass-market jewellery is laboratory-created.

Ministry of Gems sells only natural, earth-mined stones. That is our position and I will not dress it up as a moral verdict: laboratory-grown gems are a legitimate product, they are real chemistry, and someone who buys a disclosed lab-grown alexandrite for a fraction of the natural price has done nothing wrong and has bought a lovely thing. What is intolerable is a lab-grown stone sold at a natural price, or a natural stone whose treatment nobody names. Our Natural vs Lab-Grown Handbook works through that decision properly.

So here is the sentence. Ask any seller, in writing: Is this stone natural or laboratory-grown, and has it been treated — if so, by what method? A good answer is one plain sentence with a named treatment in it. A bad answer is an adjective: “enhanced” on its own is not disclosure, and nor is “genuine”, which means only that the stone is what it is called. Our treatment register and gem lexicon let you check the vocabulary against something other than the person selling to you, every stone we sell carries its disclosure on a Digital Gemstone Passport, and The Certification Handbook reads the laboratory paperwork line by line.

The 1912 committee was solving a merchandising problem, not an engineering one. Nobody in Kansas City asked whether the stone allocated to August could withstand a decade of car doors, so the list distributes wearability more or less at random.

Hardness is not toughness

Two different properties get collapsed into one number and it causes real damage. Hardness — the Mohs scale — measures resistance to scratching. Toughness measures resistance to chipping, cracking and breaking. They are not the same thing and a stone can be excellent at one and poor at the other.

Topaz is the clean example: 8 on the Mohs scale, harder than spinel, and yet it has poor toughness because it cleaves, meaning a sharp knock in the wrong direction can split it along a plane. Emerald is another: 7.5 to 8 and genuinely hard, but brittle because it is riddled with fissures. Meanwhile moonstone, at only 6 to 6.5, is undone by poor toughness rather than softness. When a jeweller tells you a stone is “hard enough”, ask about toughness too.

There is a third factor nobody prints on charts: stability. Some stones dislike light, heat or chemistry regardless of how hard they are. Amethyst can fade under prolonged strong light. Some heated zircon drifts back toward brown in bright light. Peridot dislikes acids, including long-term acidic perspiration. Turquoise is damaged by cosmetics and skin oils. Hardness will not save any of them.

The twelve months, sorted by what they can actually survive

Wear it daily, on a hand, without thinking: diamond at 10; ruby and sapphire at 9 with excellent toughness; alexandrite at 8.5 with excellent toughness; spinel at 8. These five are the genuinely carefree entries on the list, and it is no accident that three of them — diamond, ruby and sapphire — are the classic engagement-ring stones.

Wear it daily with mild sense: aquamarine at 7.5 to 8; tourmaline at 7 to 7.5, keeping it away from heat; amethyst and citrine at 7, citrine with good toughness and amethyst wanting a repolish once in a long while; garnet across 6.5 to 7.5, better in a protective setting toward the lower end. Topaz sits here too at 8, but only in a setting that shields it from knocks, because of the cleavage.

Occasional wear, or a pendant and earrings: peridot at 6.5 to 7, which GIA specifically does not recommend for daily ring wear; tanzanite at 6 to 7, which abrades easily and which GIA steers toward earrings and pendants; zircon at 6 to 7.5, which abrades rather than shatters; moonstone at 6 to 6.5 with poor toughness; sardonyx and bloodstone at 6.5 to 7.

Handle with real care: opal at 5 to 6.5, vulnerable to heat and sudden temperature change; turquoise at 5 to 6, chemically fragile; pearl at 2.5 to 3, the most delicate mainstream gem there is. Emerald belongs in this group in practice despite its hardness, because of brittleness and filler.

The three-stone months are an escape hatch

Here is the most useful practical consequence of the whole list, and it is a gift the amendments handed us. Three months have three stones, and in two of those months the newest addition is the most wearable one.

An August baby who wants an engagement ring should not be given peridot; show them spinel, which is 8 Mohs, rarely treated, and was added to the list by Jewelers of America and AGTA in June 2016. A June baby who wants a ring should be steered from moonstone and pearl toward alexandrite, which at 8.5 with excellent toughness is one of the best ring stones on the chart — budget permitting, which it frequently does not, in which case a pendant beats a doomed ring. December has no strong daily-wear option among tanzanite, turquoise and zircon.

Setting choice buys you a grade or two. A bezel — metal wrapped around the girdle — protects a vulnerable stone far better than claws, and a slightly recessed setting keeps the table below the knuckle line where most impacts land. It will not turn an opal into a sapphire, but it will meaningfully extend the life of a 6.5-Mohs stone on an active hand. Our Coloured-Stone Engagement Ring Handbook covers those trade-offs in detail.

Cleaning: the short list that prevents most damage

Almost every ruined stone I see was ruined by cleaning, not by wearing. The rules are short.

Never put these in an ultrasonic cleaner or a steamer: emerald, opal, peridot, tourmaline, topaz, turquoise, pearls, and anything you know or suspect to be fracture-filled, dyed or glass-filled. Keep acids away — lemon juice will damage a glass-filled ruby, a fracture-filled or dyed sapphire, turquoise and peridot. No hot water on filled emerald. Perfume and cosmetics before pearls and turquoise, not after. Store opal and pearls apart from harder stones in soft pouches. For anything treated or heavily included, warm water, plain soap and a soft brush is the whole procedure. The Care & Heirloom Handbook is the long version.

Most birthstone charts give no numbers at all. That is understandable — coloured stones are priced individually and a single figure would be a lie — but unhelpful when you are working out whether A$2,400 is generous or absurd. So here are ranges, each with its provenance attached — and note that the published trade figures that follow are quoted in US dollars.

Where the numbers come from, and how far to trust them

Coloured-stone pricing has no equivalent of a share price. There is no exchange, no daily fix and no audited index. What exists is trade guides, dealer price lists, published averages from bodies such as the International Gem Society, and auction results — and these four sources disagree with each other routinely, often by a factor of several.

That is not dishonesty. Two stones of the same species, weight and month can differ tenfold on colour, clarity, cut, origin and treatment. Read every range below as the width of the market rather than a prediction about a particular stone, and note the dates: a figure from 2007 or 1993 is worth having, provided you know its vintage.

The honest ranges

Alexandrite is the most price-sensitive stone on the list and the one where published figures vary most. The International Gem Society lists top-quality averages of roughly US$1,818 per carat under one carat and about US$6,667 per carat between one and two carats. Trade price guides put fine quality considerably higher — on the order of US$7,000 to US$20,000 per carat — with outstanding stones quoted from US$15,000 to well over US$100,000 per carat. Those spreads are driven by size, the completeness of the colour change, and origin, with Russian material at one end and African at the other. Present anyone quoting you a single number for alexandrite with a raised eyebrow.

Spinel spans an enormous honest range: commercial red material sits around US$100 per carat, while top Burmese red runs US$8,000 to US$15,000 per carat and beyond. Given that spinel is very rarely treated, the lower end of that span is one of the better value propositions in coloured stones, which is a sentence I do not write often.

Tanzanite is more orderly, being a single-source stone. Top vivid material retails at roughly US$450 to US$700 per carat, with fine three-to-five-carat stones quoted in a band from about US$350 to US$1,100 per carat depending on saturation.

Black opal from Lightning Ridge is where Australian figures get exciting and least verifiable. Gem grades are quoted at US$3,000 to US$15,000 per carat, with record stones around US$20,000 per carat. These are trade retail figures rather than audited data, and opal is cut in irregular shapes that make per-carat comparisons rougher than they are for faceted stones. Take the range as directional.

Sapphire is priced less by a per-carat table than by the treatment question. Trade estimates hold that 90 to 95 per cent of commercial sapphire is heated, and that unheated stones carry premiums of roughly 30 to 50 per cent over comparable heated material, rising to 200 to 300 per cent for fine stones above five carats. Once again: trade estimates, not laboratory-audited figures, and GIA itself commits only to saying heat is common. If you want to see what that premium buys in practice, our unheated sapphires sit alongside the heated Ceylon stones and you can compare them directly.

The auction headlines, and why they are not your market

The record results are worth knowing because clients arrive quoting them, usually having drawn precisely the wrong conclusion.

The per-carat record for ruby belongs to the Sunrise Ruby, a 25.59 ct Burmese stone sold at Sotheby’s Geneva on 12 May 2015 for US$30.3 million — about US$1.19 million per carat. The total-price record went to the Estrela de Fura, a 55.22 ct Mozambique ruby cut from a 101 ct rough found in July 2022, which made US$34.8 million at Sotheby’s New York on 8 June 2023, or roughly US$630,288 per carat. Note the shape of that: the larger stone made more money in total and less per carat, which tells you something true about how rarity actually works.

Spinel’s record is the Hope Spinel, 50.13 ct, sold at Bonhams London on 24 September 2015 for £962,500 — about US$1.47 million, or roughly US$30,000 per carat, against a previous per-carat record of US$16,000 set in 2013. And for June, the La Peregrina natural pearl necklace from Elizabeth Taylor’s collection made US$11.8 million at Christie’s New York in 2011.

These describe a market of a few dozen participants worldwide buying objects of documented historical significance, and are about as relevant to a birthday budget as a Formula One lap time is to your drive home. What they do show is the shape of the curve: value climbs disproportionately with size and with rarity of treatment, which is why a two-carat unheated stone costs far more than twice a one-carat one.

What this chapter is not

I want to be completely plain, because this is where gemstone writing most often goes wrong. None of this is investment advice. I am a gemmologist, not a financial adviser, and nothing in this handbook should be read as a suggestion that any stone will hold or increase its value.

Market figures exist and are worth knowing as context. Australia’s Argyle mine in Western Australia closed in November 2020 after producing roughly 90 per cent of the world’s pink diamonds, and the Fancy Color Research Foundation recorded pink-diamond values rising 116 per cent between 2010 and 2020, with fancy vivid pinks up around 39 per cent in the year following the closure. Sri Lanka’s gem and jewellery exports earned about US$477.7 million in 2023 and fell to roughly US$382 million in 2024, a drop of more than 23 per cent following new taxes on the industry. Both facts are true and both are informative about supply and trade conditions.

Neither is a reason to buy anything. Gemstones are illiquid, individually priced, carry a substantial spread between retail and resale, and have no guaranteed buyer. Buy a stone because you want to look at it for thirty years. If it appreciates, that is a pleasant accident, and if anybody tells you otherwise while holding a stone they would like you to purchase, you have learned something about them.

Two countries supply a surprising share of the twelve-month list, and they are the two this house has always worked between. I should declare that rather than pretend to neutrality: my family have been in the Ceylon gem fields across three generations since the 1960s, and I assess stones in Sydney.

Ceylon: the jewel box of the Indian Ocean

Sri Lanka’s export authority positions the island as the world’s most important source of high-quality sapphire, and its ground yields some seventy-five gem varieties — a spread no other island comes close to. That is a claim I have an obvious interest in repeating, so take it with its source attached. GIA calls it the jewel box of the Indian Ocean, and the island has been mined for sapphire for more than two thousand years.

Count how many months that touches. September sapphire, of course. June moonstone, where Sri Lanka and India are the two important sources and Ceylon is the classic one. August spinel, from the Ratnapura district, which has produced it for centuries. December zircon, from Elahera. Alexandrite for June and ruby for July are both produced there too. And padparadscha — the pink-orange sapphire that has no place on any birthstone list and steals a great many September buyers anyway — is essentially a Ceylon speciality. If that stone tempts you, The Padparadscha Handbook is the volume for it.

Sri Lanka’s gem exports are regulated by the National Gem and Jewellery Authority, which administers export licensing — part of why Ceylon material tends to arrive with a clearer paper trail. The trade is not enormous by global standards, earning about US$477.7 million in 2023 and roughly US$382 million in 2024 after new taxes, and GIA estimates that artisanal, small-scale miners supply some 80 per cent of the world’s gems. Buying a Ceylon sapphire usually means buying, at some remove, from a small operation working a pit by hand. Our Provenance Handbook deals with what can honestly be traced along that chain.

Australia’s own months

October is Australia’s month outright. Opal was proclaimed Australia’s national gemstone by Governor-General Bill Hayden on 27 July 1993 — you will see 23 July printed in places, but the Department of the Prime Minister and Cabinet gives the 27th. Australia has been credited with around 95 per cent of world precious-opal production, a figure from a 1993 United States Geological Survey assessment that is still widely repeated, including on government pages. It deserves its vintage attached: Ethiopian production since 2008 has certainly eroded that share, and no rigorous current split has been published. Lightning Ridge produces black opal, White Cliffs and South Australia’s Coober Pedy, Andamooka and Mintabie produce white, and boulder opal comes from Queensland and nowhere else on Earth. You can see what we hold in the opal collection.

September has an Australian chapter too. In the 1980s Australia supplied roughly 70 per cent of the world’s sapphires — estimates run as high as 70 to 90 per cent of commercial supply — chiefly from the New England fields around Inverell and Glen Innes in New South Wales and Queensland’s Anakie and Rubyvale gemfields. That share is far smaller today, but the stones are still being cut, and Australian sapphire has a character of its own: often inkier, often teal or parti-coloured, and increasingly sought for exactly that. Our Australian sapphires sit deliberately beside the Ceylon material.

Elsewhere on the list: December zircon is mined at Zircon Hill in the Harts Range of the Northern Territory. June’s South Sea cultured pearls are farmed from Australia’s northern coast through Indonesia and the Philippines. And April had, until recently, the most Australian story of all — the Argyle mine in Western Australia, which supplied about 90 per cent of the world’s pink diamonds before closing in November 2020.

A checklist for buying any birthstone well

Everything in this handbook reduces to seven questions. Ask them in this order.

One: which list am I using? American or British, and is the stone I have been offered actually on it. Blue topaz in December and a two-stone August are the two places this goes wrong most often.

Two: is it natural or laboratory-grown? Ask for the answer in writing. Both are legitimate; the price difference is enormous.

Three: has it been treated, and by what method? A named method in one plain sentence. “Enhanced” is not an answer.

Four: what will I do while wearing it? Match the stone to the hand, not the hand to the poster. If the month’s stone is too soft for daily wear, use the three-stone months, the anniversary chart, or simply choose something else — nobody is checking.

Five: how must I clean it? If the seller cannot tell you whether the stone tolerates an ultrasonic, they do not know what they sold you.

Six: what documentation comes with it? For anything of consequence, an independent laboratory report; for everything, a written record of species, origin and treatment that you keep. Every stone we sell carries a Digital Gemstone Passport recording exactly that.

Seven: does it look right to me? After all the paperwork, this is still the question that matters. Colour preference is not a technical failing. A stone you love at 6.5 Mohs, worn in earrings, will give you more pleasure over thirty years than a technically superior stone you chose because a chart told you to.

If you want a second opinion on any of it — including on a stone you are considering buying elsewhere, which we are perfectly happy to look at — talk to our gemmologist. That is what the free library is for.