October has two birthstones, and they are opposites. Opal is the most fragile stone on the entire birthstone list and the only one that contains water. Tourmaline is tough, comes in every color, and will survive daily wear.

Which you should buy depends almost entirely on what piece you want. And if you buy opal, there is one question that decides whether your necklace survives a shower.

Quick Decision

Opal Is the Only Gem That Can Dry Out

Opal is not a crystal. It is a hardened silica gel, and it contains water — typically 6 to 10 percent of its weight, sometimes much more. That single fact drives everything about owning one.

• Opal can craze — develop a network of fine surface cracks — if it dries out or meets a sudden temperature change.
• It is damaged by heat, dry air, strong light over long periods and rapid temperature swings.
• At 5.5 to 6.5 Mohs it is softer than household dust, so it abrades in daily wear.

No other birthstone has this property. Every other stone on the list is a crystal with fixed chemistry; opal is closer to a very old, very beautiful set gel.

The Opal Trap: Solid, Doublet or Triplet

This is the single most important question when buying opal jewelry, and most listings do not answer it clearly.

A triplet looks spectacular. The dark backing makes the color pop and the clear cap magnifies it, so a triplet can look better than a solid opal costing ten times more.

But a triplet is a sandwich held together with glue. Water seeps between the layers, clouds them, and eventually separates them. Triplets must not be submerged, worn while swimming, or cleaned in water.

What Drives Opal’s Price

Play-of-color is the flashing rainbow effect, and it is not pigment. It is produced by microscopic silica spheres diffracting light — a structural effect, like the color in a soap bubble or a butterfly wing.

1. Body tone. The background the color sits against. Black opal is the most valuable, then semi-black, then crystal (translucent), then white. The same play-of-color looks far brighter against dark.
2. Brightness. How vivid the flashes are. This matters more than pattern.
3. Pattern. Broad, organized patterns such as harlequin command large premiums; pinfire and small specks are common.
4. Color range. Red is the scarcest flash color and adds the most value. Blue and green are the most common.

Look at an opal from several angles and in different light before buying. Play-of-color changes with the viewing angle, and a stone that flashes from one direction may be dull from another.

Australian and Ethiopian Opal Are Not the Same

Most precious opal has historically come from Australia, which produces stable material including the finest black opal.

Ethiopian opal, which became widely available more recently, is mostly hydrophane — it actively absorbs water. Put a hydrophane opal in water and it can turn transparent and temporarily lose its play-of-color, returning as it dries. It can also absorb oils, soaps and dyes, which may permanently discolor it, and drying unevenly can cause crazing.

Ethiopian opal is genuine opal and often spectacular for the money. But it needs stricter care than Australian material, and dyed Ethiopian opal sold as natural is a known problem.

Opal Care: The Hard Rules

• Never use an ultrasonic or steam cleaner. This one is absolute.
• Do not soak it — especially a doublet, triplet or hydrophane stone. Wipe with a soft, slightly damp cloth.
• Avoid sudden temperature changes. Do not take it from a hot car into cold water.
• Avoid long periods in very dry air or direct heat.
• Put jewelry on last, after perfume, hairspray and lotion.
• Store it away from harder stones, which will scratch it.
• Take it off before swimming, showering, cleaning or the gym.

Tourmaline: The Practical October Stone

If the recipient wants a ring, buy tourmaline.

At 7 to 7.5 on the Mohs scale with reasonable toughness, tourmaline survives daily wear far better than opal. It also comes in a wider range of colors than any other gem species — pink, green, blue, yellow, red, brown, black, and bi-color stones with two or three colors in one crystal.

Watermelon tourmaline is the best known of these: pink at the center, green at the rim, usually cut as a slice to show both.

Paraíba: another trade name to treat carefully

Paraíba tourmaline is a copper-bearing material with an intense neon blue-green. It was first found in Paraíba, Brazil, and the finest stones are extraordinarily expensive.

Similar copper-bearing tourmaline has since been found in Mozambique and Nigeria. Much of the trade now uses “Paraíba” as a type name rather than a strict locality, which means two stones with the same name can come from different continents at very different prices.

Most tourmaline is untreated or lightly heated. Some material is irradiated to improve color, which should be disclosed.

Synthetic and Imitation Opal

Lab-created opal exists and has the same silica-sphere structure as natural opal. It is genuine synthetic opal and must be disclosed as laboratory-created. Under magnification, it often shows an unnaturally regular, columnar pattern.

“Opalite” is glass. It is not opal and should never be sold as such. Plastic imitations also circulate. Under the FTC Jewelry Guides, laboratory-created and imitation stones must be described accurately.

Buying an Opal Birthstone Necklace: What to Check

1. Solid, doublet or triplet — in writing. This is the most important question on the page.
2. Origin, and whether it is hydrophane, especially for Ethiopian material.
3. Natural, lab-created or imitation.
4. Body tone and brightness. Look at it under different light and from several angles.
5. Any dye treatment, which should be disclosed.
6. The setting. A bezel protects the edges, which is where opal chips.
7. The piece type. A pendant or earrings for daily wear. If it must be a ring, accept that it is occasional-wear jewelry.

The “Opal Is Bad Luck” Myth

You will meet this one. The superstition that opal brings bad luck unless it is your birthstone is often traced to a popular 19th-century novel in which an opal plays an unlucky role, and it is widely said that rival gem dealers were happy to help the idea spread.

Before that, opal had a long reputation as a stone of hope and good fortune. The superstition is modern, literary and commercial, not ancient.

Meaning and Tradition

Opal is traditionally associated with creativity, hope and inspiration, and it is the 14th wedding anniversary gem. Tourmaline is associated with protection and balance, and it is commonly given for the 8th anniversary.

As with every birthstone, treat the symbolism as tradition and gift sentiment rather than fact about the stone.

Frequently Asked Questions