October Birthstones: Opal and Tourmaline
If you're lucky enough to be born in October, you get not one but two of the most colorful, mesmerizing gems out there. Opal and tourmaline aren’t just beautiful — they’re a whole spectrum of color and mystery, with some pretty cool science.
Let’s get into it.
🔮 Opal: Color That Plays
Opal doesn’t just show color — it moves and shifts it. The term for this is play-of-color, and it’s what makes precious opal so iconic. Opal is considered pseudochromatic, as its rainbow flash is all about structure.
What Even Is Opal?
Opal is a mineraloid — not a true mineral — made of hydrated silica. Its internal structure contains microscopic silica spheres. In precious opals, these spheres are stacked just right to diffract light, creating that famous rainbow shimmer. The size and arrangement of the spheres determine what colors you see.
Precious opal has play-of-color (think lightning flashes or oil slicks).
Common opal doesn’t — but it can still be stunning in different shades (think pink opal or andean blue opal).
Fire opal is usually orange, red, or yellow and may or may not have play-of-color.
Boulder opal is a type of opal still attached to its host rock and often has gorgeous contrasting patterns. It's one of my favorites.
Because opal contains water, it can be sensitive to changes in humidity and temperature. They’re perfectly wearable — they just appreciate a little care.
🌈 Tourmaline: The Rainbow Stone
Tourmaline is basically the overachiever of the mineral world when it comes to color. It comes in almost every shade you can think of — pink, green, blue, purple, yellow, black, even colorless. It’s so colorful that one of the most famous varieties is actually bi-colored: watermelon tourmaline, with green edges and a pink core that really does look like a slice of the fruit.
So how does it get all those colors?
The Science Bit:
Tourmaline is allochromatic, which means it gets its color from trace elements and impurities. Different elements = different colors:
Iron tends to make it green or blue (like in indicolite).
Manganese gives it pinks and reds (like rubellite).
Chromium or vanadium can create vibrant greens, like in chrome tourmaline.
There are also multi-color tourmalines that formed as the chemical conditions shifted during growth. That’s why you might find a single crystal with pink, green, and clear zones — all in one gorgeous piece.
Two Gorgeous Choices
October’s two birthstones are a study in contrast — and complement. Tourmaline is structured, stable, and crystal-clear in its color origins. Opal is amorphous, watery, and playful. One holds its color in place; the other dances with it. Both are utterly unique. And if you're like me, you're a little jealous of those born in October for having these two beauties as your birthstones.