September birthstone

September's main stone — the sapphire

Nine sapphires out of ten in a display case have been heated — held at well over a thousand degrees to deepen the blue and dissolve the milky haze inside. The trade has done this for decades, the change is permanent, and a heated stone is still a genuine sapphire; the only rule is that the seller has to say so. Untreated stones with a lab report behind them cost several times more for the same look, and that is the single biggest reason two near-identical rings carry wildly different price tags.

Colour names on the tag are salesmanship, not grading. “Cornflower”, “royal blue” and the famous “Kashmir velvet” describe an impression, and only the last one points at a real place — a Himalayan deposit whose workings were exhausted in the 1880s, about a hundred and forty years ago, which is why Kashmir stones now surface mainly at auction. Most sapphires sold today come out of Sri Lanka, Madagascar and Australia, and a good Ceylon stone seen in daylight will beat a mediocre one with a romantic label.

Sapphire carries more folklore than most stones on this chart — clear thinking, safe journeys, fidelity — and none of it survives a moment's checking; for anything touching health the person to see is a doctor, not a jeweller. Say that once and the stone is left with what it genuinely has, which is not nothing: Mohs 9, a blue that behaves in daylight and lamplight alike, and a September date pinned to it by a committee in 1912. It catches the light on an ordinary Tuesday, and that is the whole of the job.

What the sapphire actually is

Sapphire is corundum: crystallised aluminium oxide, Mohs 9, harder than anything else you are likely to own except a diamond. Pure corundum is colourless, a trace of iron and titanium turns it blue, and the same mineral coloured red by chromium is not called sapphire at all but ruby — which is how one mineral came to occupy two months of the chart. The rough comes from gem gravels in Sri Lanka, basalt fields in eastern Australia and, since the 1990s, very large finds in Madagascar.

Not everything sold as sapphire is sapphire, and the problem comes in two grades. Flame-fusion synthetic corundum has been made since 1902: chemically identical, grown in hours, worth a few pounds a carat, and perfectly legal to sell as long as the word “created” or “lab-grown” sits on the label. It is also easy to spot once somebody looks — the growth lines curve and the bubbles are round, where a mined stone shows straight zoning and mineral inclusions, so synthetics tend to give themselves away by looking a little too orderly. Cheaper still are blue glass, doublets glued from a slice of stone on a glass base, and diffusion-treated stones whose colour is a skin-deep layer that a recut would take off. The defence is boring paperwork: ask what treatment the stone has had, get the answer in writing, and for anything expensive insist on a report from an independent laboratory.

The September stone as a gift

A September birthday makes sapphire the obvious present, and it is a forgiving stone for one: Mohs 9 means it survives being worn every day by someone who never takes jewellery off to wash up. Blue is what people expect, but corundum also grows yellow, green, peach-pink and nearly colourless, and “fancy” sapphires cost a fraction of good blue material — the same mineral, a lower price, and less risk of buying the fifth blue pendant she already owns.

Sapphire also runs on a second track: it heads the Virgo list for reasons that have nothing to do with the jewellers’ chart, which makes a neat double for anybody born through 22 September — from the 23rd the sign changes and the month stone does not. One last practical thing, wherever you buy: get the treatment written on the receipt. “Heated” is normal and worth saying out loud; “unheated” is worth several times the price and worth a laboratory report, and a shop that will put neither in writing has answered a different question rather well.

Where the month chart came from

Nothing in geology or astronomy ties a mineral to a page of the calendar. The chart everyone quotes was agreed by American jewellers in 1912, in Kansas City, so that shops across the country would sell one list rather than twelve. It has been edited since: alexandrite, citrine, tourmaline and zircon were added in 1952, and tanzanite joined December as late as 2002 — thirty-five years after the stone was first dug up in Tanzania.

So when two shops give you two different stones, neither of them is lying. British lists keep bloodstone for March where American ones print aquamarine. June carries pearl from the old custom and moonstone plus alexandrite from the newer one. Read any of these charts as a custom with a paper trail — a dated commercial agreement — and not as a fact about the person born that month.

Month or star sign: two different lists

The month stone and the zodiac stone belong to different traditions: one is a jewellers' chart, the other is astrology, where the stone is derived from the ruling planet and the element. Two signs fall inside September: Virgo stones (through September 22) and Libra stones (from September 23). We do not repeat the astrology here — that reading lives on the sign pages.

At a glance

Frequently asked questions

The month-by-month chart is a 20th-century jewellery custom, not science: no link between a mineral and a birth date has ever been demonstrated. Stones do not heal and do not steer events — health questions belong with a doctor, not with a pendant. The stone images on this page are generated illustrations, not photographs of particular specimens.