What is the birthstone for October? A full guide to the month's gemstones and symbolism.

People born in October can have one of two astrological signs: Libra (born between October 1 and 22) and Scorpio (born between 23 and 31). The marigold and cosmos also represent those born in October.

Additionally, each month has at least one birthstone, while others have more. For instance, May has the emerald, while June has alexandrite, pearl and moonstone.

But what about October's birthstone? Actually, the month has two.

Here's what you need to know about October's birthstones, including their colors, symbolism, meanings and more.

October birthstones

October has two birthstones: opal and tourmaline.

Opal is the traditional birthstone for October. It is believed the stone was originally found in India, where it was given the name "upala," or "precious stone" in Sanskrit, according to the Geological Institute of America.

This gemstone is well-known for its "play-of-color," or ability to shift hues. Rough opals appear white, but when polished, they show a rainbow kaleidoscope on their surface.

Opals can be found across the globe, with Australia being a major source for the birthstone. Other sites that produce opals include Ethiopia, Mexico, Brazil, central Europe, Honduras, Indonesia, Madagascar, Peru, Turkey and the U.S., according to the Geological Institute of America.

In ancient Greece, it was believed opals could protect against disease and were given as "the gift of prophesy," according to GIA. Opal has also been thought to symbolizes purity, hope and truth.

Besides being a birthstone, opals are given as fourteenth wedding anniversaries gifts.

What color is my birthstone? Learn which gemstone represents each month and what it means.

Tourmaline is the modern birthstone for October.

The gem comes in many different varieties, including pink, red, green, blue, violet and black. This is fitting since tourmaline's name derives from the Sinhalese word "toramalli," which means "stone with mixed colors," according to GIA.

Like other stones, tourmaline has been mistaken for others in the past. For instance, the "Caesar’s Ruby" is not actually a ruby; it is, in fact, a red tourmaline, according to GIA.

Tourmaline is primarily mined in Brazil, but it can also be found in Afghanistan, Pakistan, Kenya, Madagascar and Mozambique, as well as in California and Maine.

Thanks to its wide range of hues, the symbolism of tourmaline depends on its color. For example, pink tourmaline has been associated with love and compassion, while green tourmaline with courage and confidence.

The gemstone is also given as a gift for the eighth wedding anniversary.

Want to learn more about other month's birthstones?

April | May | June | July | August | September | October | November | December | January

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This article originally appeared on USA TODAY: October birthstone: A full guide to the opal and tourmaline gemstones