October Birthstone: Opal and Tourmaline Explained

October Birthstone: Opal and Tourmaline Explained

October is one of the months that gets a choice, and it is a wide one. Opal is the historic birthstone, prized since Roman times, and it behaves unlike any other gem in the case. Tourmaline joined the list in 1952 when the American National Retail Jewelers Association expanded the modern lineup, and it brought with it a color range no single species can match. This guide explains both stones - their colors, their meaning, and the very different care each needs - and the hard-wearing options in the same palette for a piece you will wear every day.

Key Takeaways

• October has two birthstones: opal, the ancient original, and tourmaline, added to the modern American list in 1952.
• Opal is not a crystal at all. It is hydrated silica containing up to about 20 percent water, which is why it needs more care than any other birthstone.
• Tourmaline has the widest color range of any gemstone species, from watermelon bicolors to the electric neon blue-green of Paraiba.
• Durability separates them: opal sits at 5.5 to 6.5 on the Mohs scale and scratches easily; tourmaline is a much sturdier 7 to 7.5.
• For an October ring worn daily, a pink sapphire or ruby gives a similar palette at Mohs 9, the same hardness class as the toughest gems.

Two Stones, Two Very Different Personalities

For anyone shopping for an October birthday, the practical decision comes down to what the piece will do. One of these stones can live on a hand that washes dishes. The other really cannot. Understanding why comes down to how each one is built.

Opal: The Stone That Contains Water

Opal is the outlier of the gem world. It has no crystal structure; it is amorphous hydrated silica, formed as water carrying dissolved silica seeps through rock and leaves microscopic spheres behind. Those spheres are the whole story: when they are uniform in size and neatly stacked, they diffract light into the shifting colors that gemologists call play-of-color. When they are irregular, you get common opal, pretty but without the fireworks.

That structure explains everything about how opal behaves. Its water content can run from about 3 to 21 percent, which is why sudden changes in temperature or humidity can cause fine surface cracks known as crazing. It explains the low hardness, 5.5 to 6.5 on the Mohs scale, well below the 7 of ordinary household dust. And it explains the price gap between types.

The main varieties:

• White or light opal, the most common, with play-of-color on a pale body.
• Black opal, with a dark body tone that makes the colors blaze; the finest historically come from Lightning Ridge in New South Wales and are the most valuable opal of all.
• Boulder opal, still attached to its ironstone host rock, which gives natural dark backing and structural support.
• Fire opal, the warm orange to red Mexican variety, often transparent and frequently faceted rather than cut as a cabochon.
• Ethiopian opal, from deposits developed since the 2000s, which broadened the market considerably.

Australia was for a century the source of the overwhelming majority of the world's precious opal, and Australian black opal remains the benchmark.

Care. Never use an ultrasonic or steam cleaner on opal. Wash with mild soap and lukewarm water, dry gently, and store away from heat and direct sunlight. Doublets and triplets, opal layered onto a backing, must never be soaked, since water can separate the layers. Opal earrings and pendants live long lives. Opal rings worn daily do not.

Tourmaline: The Most Colorful Species on Earth

If opal is one stone doing something extraordinary, tourmaline is a whole family. It is not a single mineral but a group of related boron silicates whose chemistry varies enough to produce nearly every color, sometimes several in the same crystal.

Egyptians had a legend for it: tourmaline travelled up from the center of the Earth along a rainbow and collected all its colors on the way. Miners in the 1500s were less poetic; Portuguese explorers in Brazil sent home "emeralds" and "rubies" that were in fact green and pink tourmalines, a confusion that persisted until the 1800s.

The varieties collectors chase:

• Rubellite, the pink to red variety, and the most valuable of the traditional colors.
• Indicolite, blue tourmaline, genuinely rare in strong saturation.
• Verdelite, the green that fooled the Portuguese.
• Watermelon tourmaline, a bicolor crystal with a pink core and green rim, usually sliced across so both show.
• Paraiba tourmaline, discovered in Brazil in 1989 and colored by copper, producing a neon blue-green unlike anything else in gemology. Fine Paraiba is among the most expensive colored stones in the world per carat.

At 7 to 7.5 on the Mohs scale, tourmaline is a legitimate everyday stone, comparable to quartz or a garnet, though it wants a protective setting if it is going on a hand. It is also the traditional gem of the eighth wedding anniversary, while opal marks the fourteenth; our anniversary jewelry by year guide maps the full tradition.

Which October Stone Should You Choose?

	Opal	Tourmaline
Mohs hardness	5.5 to 6.5	7 to 7.5
Best formats	Pendants, earrings, occasional rings	Rings, pendants, earrings
Color	Shifting play-of-color	Widest range of any gem species
Cleaning	Mild soap only, never ultrasonic	Warm soapy water, avoid heat
Typical treatments	Sometimes impregnated or backed	Often heated; some clarity enhanced

The short version: choose opal for a piece that will be worn occasionally and treasured, and tourmaline if it needs to work harder. And ask about treatments for both, since disclosure is not optional and does change value and care.

October Colors With Heirloom Durability

Here is the part of the conversation we have across the counter most often. When someone wants an October birthstone piece for daily wear, a ring especially, we are honest: neither opal nor tourmaline is the toughest option, and there are stones in the same color families that will outlive both.

Our house specialty is corundum, sapphire and ruby, at 9 on the Mohs scale, harder than every natural gem except diamond. It happens to cover October's palette closely.

If pink or rubellite tourmaline is the look, a pink sapphire gives the same blush at nearly twice the scratch resistance.

If the deep red end of tourmaline is the draw, ruby is its durable cousin, and it shows beautifully in a halo.

And for a piece that carries real color across the wrist, an alternating ruby and diamond tennis bracelet does what a tourmaline line bracelet would, with none of the worry.

For the warm golden end of the October range, a yellow sapphire delivers autumn color that will never scratch, and it looks especially rich in warm metals like rose gold.

Explore the full sapphire collection, our rings, earrings, bracelets, and necklaces, or read the sapphire buying guide for how to judge colored stones properly.

If your heart is genuinely set on a fine opal or a Paraiba tourmaline, tell us. Sourcing specific colored stones for clients is part of what our gem desk does, and our GIA-graduate jewelers will show you options side by side rather than talking you into something else.

See October's Colors in Person

Color is the one thing screens cannot deliver honestly. Opal's play-of-color shifts as you move it; tourmaline can look like two different stones from two angles; sapphire and ruby change character between daylight and lamplight. Ten minutes at the counter at 888 Brannan Street settles what an hour of scrolling cannot. Every purchase includes 10-day returns and exchanges.

Frequently Asked Questions

What is the October birthstone?

October has two: opal, the traditional stone, and tourmaline, added to the modern American birthstone list in 1952. Both are accepted, and either can be given for an October birthday.

Is opal durable enough for an engagement ring?

Generally no. Opal measures 5.5 to 6.5 on the Mohs scale, softer than everyday dust, and it can craze with temperature changes. For a daily-wear ring in October colors, tourmaline is sturdier, and pink sapphire or ruby is sturdier still at Mohs 9.

What colors does tourmaline come in?

Nearly all of them. Tourmaline has the widest color range of any gemstone species, including pink rubellite, blue indicolite, green verdelite, bicolor watermelon, and the rare neon Paraiba.

How do you clean opal jewelry?

With mild soap and lukewarm water only. Never use an ultrasonic or steam cleaner, never soak a doublet or triplet, and store opal away from heat and direct sunlight.

Which October birthstone is more valuable?

It depends entirely on quality. Fine black opal and fine Paraiba tourmaline both rank among the most expensive colored stones per carat, while common opal and ordinary green tourmaline are modest.