Abirthstone is agemstone that represents a person's birth period, usually the month. Birthstones are often worn asjewelry or apendant necklace.

The first-century historianJosephus believed there was a connection between the twelve stones inAaron's breastplate (signifying theTwelve Tribes of Israel, as described in theBook of Exodus), the twelve months of the year, and the twelve signs of thezodiac.^{[1]: 275–306} Translations and interpretations of the passage inExodus regarding the breastplate have varied widely, with Josephus himself giving two different lists for the twelve stones.^{[2]: 130–131}George Frederick Kunz argues that Josephus saw the breastplate of theSecond Temple, not the one described in Exodus.St. Jerome, referencing Josephus, said the Foundation Stones of theNew Jerusalem (Revelation 21:19–20) would be appropriate for Christians.^[3]: 294

In the eighth and ninth centuries, religious treatises associating a particular stone with anapostle were written so that "their name would be inscribed on the Foundation Stones, and his virtue."^[3]: 299 Practice became to keep twelve stones and wear one a month.^[3]: 298 The custom of wearing a single birthstone is only a few centuries old, though modern authorities differ on dates. Kunz places the custom in eighteenth-centuryPoland, while theGemological Institute of America starts it in Germany in the 1560s.^[3]: 293

Modern lists of birthstones have little to do with either the breastplate or the Foundation Stones of Christianity. Tastes, customs, and confusing translations have distanced them from their historical origins,^{[4][3]: 310} with one author calling the 1912 Kansas list (see below) "nothing but a piece of unfounded salesmanship."^[2]: 132

Some poems match each month of theGregorian calendar with a birthstone. These are traditional stones of English-speaking societies.Tiffany & Co. published these poems "of unknown author" for the first time in a pamphlet in 1870.^[5]

In August 1912, to standardize birthstones, the (American) National Association of Jewelers (now calledJewelers of America) met in Kansas City and officially adopted a list.^[1]: 317 The Jewelry Industry Council of America updated the list in 1952^[3]: 311 by addingAlexandrite for June,citrine for November andpinktourmaline for October. They also replaced December'slapis lazuli withzircon and switched the primary/alternative gems for March. The American Gem Trade Association addedtanzanite as a December birthstone in 2002.^[6] In 2016, the American Gem Trade Association and Jewelers of America addedspinel as an additional birthstone for August.^[7] Britain's National Association of Goldsmiths created its own standardized list of birthstones in 1937.^[8] In 2021, Japanese industry associations added ten new types of birthstones.^[9]

Hinduism recognizes a similar range of gemstones associated with birth, though rather than associating a gem with a birth month, gemstones are associated withcelestial bodies.Astrology determines the gemstones most closely associated with and beneficial to a particular individual. There are nine gemstones related to theNavagraha (celestial forces including the planets, the Sun, and the Moon), known in Sanskrit asNavaratna (nine gems). At birth, an astrological chart is calculated. Specific stones are recommended to be worn on the body to supposedly ward off potential problems based on the place of these forces in the sky at the exact place and time of birth.^[10]

While the term "birthday stone" is sometimes used as a synonym for a birthstone, each day of the week is also assigned a unique gemstone, and these assignments are distinct from the monthly assignments.^[1]

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  Garnet, the birthstone for January
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  Amethyst, the birthstone for February
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  Aquamarine, the birthstone for March
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  Diamond, the birthstone for April
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  Emerald, the birthstone for May
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  Pearl, one of three June birthstones
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  Moonstone, one of three June birthstones
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  Alexandrite, one of three June birthstones
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  Ruby, the birthstone for July
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  Peridot, the modern birthstone for August
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  Sardonyx, the traditional birthstone for August
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  Spinel, a more recent (2019) alternative birthstone for August
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  Sapphire, the birthstone for September
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  Lapis lazuli, the traditional birthstone for September
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  Opal, one of two October birthstones
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  Tourmaline, one of two October birthstones
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  Citrine, one of two November birthstones
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  Topaz, one of two November birthstones
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  Turquoise, one of three December birthstones
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  Tanzanite, one of three December birthstones
• 
  Zircon, one of three December birthstones

• Birth flower

• The Curious Lore of Precious Stones, G.F. Kunz – full text online version
• Gems and Gem Minerals, Oliver Cummings Farrington – full text online version

• Birthday culture
• Gemstones in culture

• CS1 uses Japanese-language script (ja)
• CS1 Japanese-language sources (ja)
• Articles with short description
• Short description is different from Wikidata
• Use dmy dates from April 2022