The Codex

The Flower of Plenty — a citrine butterfly on an open floral band in sterling silver.
November's two birthstones are the two most transformed stones in the calendar
November's birthstones are topaz and citrine, and almost all of both have been changed by people. Most citrine is heated amethyst. Effectively all blue topaz was irradiated. What sky, Swiss... Read more...
Burning Heart — a heart-cut garnet on a blackened sterling silver band.
Garnet is six minerals, and the red one is the least interesting
January's birthstone is garnet — not one stone but a family of at least six minerals, running from raspberry rhodolite to green tsavorite that outprices emerald. And the one thing... Read more...
Night Amethyst — a purple amethyst set against a blackened rhodium band in sterling silver.
Amethyst was one of the five precious stones until somebody found Brazil
February's birthstone is amethyst — ranked with diamond, ruby, emerald and sapphire until nineteenth-century Brazilian deposits collapsed the price overnight. Why its purple is radiation damage, why it fades in... Read more...
Sapphire Flight — a blue sapphire bird ring in sterling silver, with matching earrings.
September's birthstone is sapphire, and sapphire is colourless
September's birthstone is sapphire — the same mineral as ruby, colourless until iron and titanium contaminate it. Why almost every sapphire on sale has been heated, what diffusion treatment actually... Read more...
Pink Star — a lab-grown star ruby cabochon holding a six-rayed line of light, set in a two-tone floral band.
July's birthstone is ruby, and ruby is sapphire
July's birthstone is ruby — the same mineral as sapphire, separated from it by one trace element. Why the line between pink sapphire and ruby is a trade argument rather... Read more...
Blue Antler — Swiss blue topaz set in a deer-antler necklace and ring in sterling silver.
December has four birthstones, and the newest one is younger than the moon landing
December's birthstones are turquoise, zircon and tanzanite — plus blue topaz, which most shops sell you. One was unknown to science until 1967 and comes from seven kilometres of hills... Read more...
The Garden Rule ring, peridot set alongside amethyst and topaz in a botanical band.
August's birthstone comes out of volcanoes, and sometimes out of space
August's birthstone is peridot — the only common gem that arrives on earth two ways, pushed up out of volcanoes and dropped out of the sky inside meteorites. Why it... Read more...
The Zodiac Circle necklace, a natural African opal set inside a dark pavé disc with the animal worked in gold relief.
October has two birthstones, and one of them was made unlucky by a novel
October's birthstone is opal, and also tourmaline. Opal spent most of the nineteenth century being avoided as unlucky — a superstition with a traceable start date in 1829, and a... Read more...
A rainbow moonstone ring catching the soft blue glow that seems to float below the surface of the stone.
June's birthstone is three stones, and one of them changes colour
June's birthstone is pearl, moonstone and alexandrite — all three are correct. One was made by an animal, one is a trick of light inside feldspar, and one turns from... Read more...
The Zodiac Circle necklace on illustrated paper, beside the original sketch of the twelve animals.
The twelve animals, and why your year might not be the one you think
The Chinese zodiac year does not begin on 1 January. It begins at Chinese New Year, which moves between 21 January and 20 February — so a great many people... Read more...
An oval moissanite leaf ring set in sterling silver
Moissanite and diamond: what the difference actually is
Moissanite is not a fake diamond. It is a different mineral with different optics — harder to scratch than sapphire, and it throws more colour than diamond does. Here is... Read more...
A garnet heart ring in blackened silver with gold leaf detail, photographed against deep red peonies
Garnet: the stone people took with them at night
January's stone is named after a pomegranate, is not one mineral but a family of them, and turns up in green as often as red. What garnet is, where it... Read more...
A moss agate pear ring set with marquise accent stones, photographed on moss
Moss agate: the stone with a garden inside it
The green in moss agate is not moss and never was. It is mineral threaded through clear chalcedony, which is why no two stones are alike — and why it... Read more...
All twelve birthstone drop charms, January to December, laid out in a grid
Birthstones by month: what each one actually is
The modern birthstone list is a retail document from 1912, revised four times since. Here is what each month's stone actually is, where it comes from, and where the colour... Read more...
Citrine: the stone people kept where the money was counted
Most of the citrine sold in Britain began the year as amethyst. The merchant's stone label is younger than it sounds, the logic behind it is four hundred years older, and there is a plain way to tell a natural stone from a heated one. Read more...
Citrine butterfly open ring in sterling silver
Ring sizes: the number we ask for, and how to measure at home
Asi8 asks for a number between 4.5 and 10. Britain writes the same measurement as a letter, Europe as a circumference. Here is the conversion, two ways to measure your... Read more...
Green agate multi-stone ring in sterling silver
What people mean when they say a stone has meaning
Crystal meanings did not come from an ancient unbroken tradition. They came from Greek natural history, a medieval bishop's poem, Victorian gift books and a 1980s publishing boom — each... Read more...
Oval moonstone ring on a fine gold-tone band
Moonstone and the blue that isn't there
The blue light inside a moonstone is not a colour. It is an optical effect produced by layers thinner than a wavelength of light. Here is where it comes from,... Read more...
Dragon zodiac necklace with natural African opal
The twelve animals: how the Chinese zodiac became jewellery
The twelve-animal cycle is older than the calendar most people use it with, it was never really about personality, and the reason it ended up on necklaces has more to... Read more...
Natural amethyst ring in sterling silver
Amethyst: the stone that was supposed to keep you sober
Amethyst got its name from a Greek word for "not drunk", spent six hundred years on the hands of bishops, and then lost its place among the precious stones in... Read more...
Turquoise: six thousand years of being carried
Turquoise is the oldest stone humans have carried deliberately — from the Sinai mines to the Silk Road to the American Southwest. What it has meant, why it keeps meaning the same thing, and how to look after it. Read more...