November has two birthstones — topaz and citrine — and both of them are, in almost every shop, transformed material. Most citrine on the market is amethyst that was heated. Most blue topaz was colourless topaz that was irradiated and then heated. November is the most quietly modified month in the calendar.
None of that makes the stones fake. It makes them worth understanding before you buy, which is a different thing.
Citrine is usually amethyst that got hot
Citrine and amethyst are the same mineral: quartz with a trace of iron. In amethyst that iron sits in one oxidation state and natural radiation has created a purple colour centre. Take it to roughly 400–500°C and the iron changes state, the purple colour centre is destroyed, and yellow to orange comes out instead.
The change is permanent and completely stable. It is also why natural, unheated citrine is genuinely uncommon and why a very large, very cheap, very orange "citrine" is a heated amethyst — usually one that was too pale to sell as amethyst in the first place.
The tell, if you want one: heated material often runs to a reddish or brownish orange, sometimes with the colour concentrated at the point of the stone. Natural citrine is more often a paler, cooler lemon.
Blue topaz did not exist until the 1970s
Natural topaz occurs colourless, and colourless topaz is abundant and almost worthless. Natural blue topaz exists but is pale and rare.
Then the trade worked out that irradiating colourless topaz — in a linear accelerator or a nuclear reactor — creates colour centres, and a subsequent heat treatment stabilises them into blue. Effectively all of the blue topaz in the world is made this way. Treated stones are held until residual radioactivity has decayed to levels below regulatory limits, and in most markets that is a legal requirement rather than a courtesy.
The three names you will see are grades of that process:
- Sky blue — the palest, closest to a summer sky.
- Swiss blue — brighter, more saturated, the strong electric blue.
- London blue — the darkest, inky, slightly grey-green.
They are not different minerals or different deposits. They are different doses.
Imperial topaz is the one that isn't
The exception to all of this is imperial topaz — pink, orange and sherry-coloured material, mostly from Ouro Preto in Brazil, coloured by chromium rather than by anything done to it. It is the expensive end of the species by a wide margin, and it is what "topaz" meant historically before the blue material took over the shop windows.
The one real warning about topaz
Topaz is 8 on the Mohs scale, harder than quartz and harder than most things it will meet. But it has perfect basal cleavage: a single plane, perpendicular to the length of the crystal, along which a sharp knock will split it cleanly in two.
That is a genuinely different risk profile from sapphire or garnet, which have no cleavage at all. A topaz ring is not fragile in normal wear, but it is the one stone in this list where a single hard, badly angled knock can do something a jeweller cannot undo. Take it off for anything involving impact.
Also: keep blue topaz out of prolonged strong sunlight and off a steam cleaner. The colour is a colour centre, and colour centres can be undone by energy.
What we make for November
For citrine: The Flower of Plenty, a butterfly on an open floral band.
For topaz, all three blues are in the catalogue. Plain Speaking is sky blue, and the plainest setting we make. Blue Antler is Swiss blue in a deer necklace and ring. Open Current pairs sky blue topaz with amethyst as drop earrings, and Broken Light sets topaz against mystic quartz.
Every one of those product pages says the topaz is treated, on the page rather than underneath it.
The everyday version is Month in Colour: one baguette stone on a fine chain, solid 925 sterling silver plated in gold rather than plated brass. The November stone is golden yellow. It is cubic zirconia cut to the birthstone colour, not citrine. That is on the product page, not in the small print.
Everything is made after you order it, so allow up to ten days.
All twelve months, and what each stone actually is →
What citrine has been used to mean →
A birthstone is a date, not a diagnosis. Nothing here treats, prevents or cures anything.