What Is October's Birthstone?

Opal — the traditional stone: known for its "play-of-color" effect, where flashes of rainbow color shift across the stone's surface as it moves in the light, caused by microscopic silica spheres inside the stone diffracting light. Opals range from milky white common opal to the rarer, more vivid black opal. They're relatively soft and porous, so they need more careful handling than harder gems (avoiding extreme temperature changes and prolonged water exposure).

Tourmaline — the modern alternative: notable for occurring in an unusually wide range of colors, including pink, green, blue, and multi-colored "watermelon" tourmaline (pink center, green edge). It was added to the official birthstone list by the American National Association of Jewelers in 1912 as part of a broader modernization of the birthstone list, partly to give a more durable, widely available option alongside softer traditional stones like opal.

Why October has two stones instead of one: the modern list (1912) didn't replace the older traditional list — it ran alongside it, and several months (including October) ended up with both a historical stone and a newer addition retained for variety and affordability.

Related October associations: the zodiac signs spanning October are Libra (through Oct 22) and Scorpio (from Oct 23), which have their own separately associated stones in some astrological traditions, distinct from the calendar-month birthstones above.

Nearby questions in this topic include What Is Sapiosexual? and What Is the Rarest Zodiac Sign?.

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