October birthstone

October's main stone — the opal

An opal is not a crystal. It is silica that dried into microscopic spheres stacked like oranges in a crate, with water still trapped between them — anywhere from three to twenty-one per cent of the stone by weight. The flashes of green and red are not pigment: the spheres happen to sit at about the wavelength of visible light, so they split it the way the underside of a CD does. Shift the angle and a different colour comes back at you.

Three things sit in the case labelled opal and they are not equals. A solid opal is one piece of stone. A doublet is a thin slice glued to a dark backing so the colour reads stronger; a triplet adds a clear cap on top. Both are worth a fraction of a solid stone and both hate water at the glue line. Then there is “opalite”, manufactured glass with no opal in it whatsoever. None of that is illegal — it only has to be on the label, so ask which of the three you are holding before the price starts to make sense.

Photographs flatten play-of-colour, and an illustration can only hint at it: two opals at the same price can look like different species in the hand, and a stone that dazzled under shop spotlights sometimes goes quiet in daylight. Tilt it, carry it to a window, and buy the one that still works away from the lamp.

The other stones listed for October

Tourmaline is October’s second name, and it earned the slot by sheer range: no other gem grows in as many colours — pink, green, black, honey, and “watermelon” crystals that are green on the outside and pink through the middle, sliced across to show both at once. Maine and Minas Gerais pull them from the same pockets in every shade, and the copper-bearing Paraíba variety glows an almost electric turquoise. At Mohs 7 to 7.5 it is much tougher than opal, which makes it the sensible pick for a ring somebody will wear daily.

October also spans two star signs — Libra through the 22nd, Scorpio from the 23rd — and the astrological route reaches the opal from a completely different direction: balance and colour rather than the jewellery trade. Libra’s stones put it first for reasons no gem dealer would recognise. Nothing forces a choice between the two lists; they were drawn up by different people for different purposes.

What the opal actually is

Australia dug up most of the world’s opal for a century — Coober Pedy for white and crystal material, Lightning Ridge for the black opal that carries the strongest colour and the highest prices. Since 2008 a second source has reshaped the market: Welo in Ethiopia, where the stone comes out bright, cheap and hydrophane, meaning it drinks water. Soak an Ethiopian opal and it can go glassy and see-through for days before it dries back; most return exactly as they were, some craze into a web of fine cracks.

The names on the tickets repay a squint too. “Common opal”, or potch, has no play of colour at all and is sold as beads by the kilo. “Fire opal” means the orange Mexican material, which may or may not flash. “Boulder opal” is a natural seam still attached to its ironstone host — a solid stone, unlike a manufactured doublet, though the layer of colour is just as thin. Mohs 5.5 to 6.5 across the family: a steel key riding in the same pocket will leave a mark.

The October stone as a gift

Give an opal as a pendant or earrings rather than an everyday ring and nobody will be apologising in two years. It is soft, it holds water, and it dislikes everything a hand meets — knocks against doorframes, hot washing-up, bleach, ultrasonic cleaners, long spells in dry air. Kept off the hands it lasts indefinitely, and a doublet at a quarter of the price is a perfectly honest present so long as everyone knows that is what it is.

Someone at the table will bring up the old line about opals being unlucky. It came from a novel published in 1829, and the answer the trade offered at the time says everything about how seriously to take it: bad luck, apparently, except for people born in October. Minerals do not arrange anybody’s fortunes in either direction — which is the only reason the joke is safe to repeat over the wrapping paper.

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 October: Libra stones (through October 22) and Scorpio stones (from October 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.