October birthstone
Opal
The October birthstone is opal, with tourmaline as the modern alternate. Opal is hydrated silica rather than a crystal, and it contains water, typically between three and ten percent. That structure produces the play of color that makes it unmistakable, and it also makes opal the most delicate stone commonly set in antique jewelry.
- Species
- Hydrated amorphous silica
- Color range
- Body color from white to black, with play of color across the spectrum
- Mohs hardness
- 5 to 6.5
- Also this month
- Tourmaline
Opal is the signature stone of Art Nouveau. The period wanted color and effect rather than carat weight, and opal delivered a shifting, iridescent surface that no faceted stone could match. It also appears throughout Victorian jewelry, often in small cabochons set with diamonds or rubies.
Play of color comes from microscopic silica spheres diffracting light, which is why the flashes move as the stone moves. Body color, brightness, the pattern of the flashes and which colors appear all affect value, and red on a dark body is the rarest combination.
Because opal contains water it can craze, developing a network of fine surface cracks, if it dries out or is subjected to sudden temperature change. A century old opal that is still bright has survived exactly the conditions that damage most of them, which is worth something in itself.
In antique and vintage jewelry
Art Nouveau pendants and brooches with enamel and gold, Victorian cabochons ringed by small diamonds, and Edwardian pieces where opal sits against platinum lace.
Wearing and caring for it
Treat opal as the most fragile thing you own. No ultrasonic cleaner, no steam, no solvents, no sudden temperature change and no dry heat. Wipe with a soft, barely damp cloth. Take opal rings off for anything physical.
As a gift
Nothing else looks like it. Because opal is soft, a pendant, brooch or pair of earrings is a far better gift than a ring that will be worn every day.
Common questions
Why is opal so fragile?
It is not a crystal and it contains water. At 5 to 6.5 on the Mohs scale it scratches easily, and drying or thermal shock can craze the surface.
What is a doublet or a triplet?
A thin slice of opal backed, and in a triplet also capped, with other material to make it look thicker and darker. It is a legitimate construction, but it must be disclosed, and we state it whenever we find it.
Is opal unlucky?
That superstition traces to a nineteenth century novel and to jewelers of the period losing stones to breakage, not to anything about the stone. It says more about opal's fragility than about luck.
Shop the pieces
Shop opal jewelry
Antique and vintage pieces set with opal, each one a single example.
Nothing matching this is available right now. Every piece is a single example and sells once, so this changes weekly. Browse everything in stock or ask our buyers to look for it.