Birthstones — the full chart

Where birthstones came from

The oldest thread runs back to the breastplate described in the Book of Exodus, set with twelve stones for the twelve tribes of Israel. First-century writers connected those twelve to the twelve signs of the zodiac, and the practice at that stage was to own all twelve and wear each during its own period.

Wearing only the stone of your birth month is a much later habit, generally dated to early modern Europe — George Kunz traced it to eighteenth-century Poland. The version most people know today is younger still: the National Association of Jewelers fixed the American list in 1912, and that commercial standard is what the trade has used since.

Month, or zodiac sign?

They are two different systems and they do not line up, because zodiac signs straddle two calendar months. Someone born on October 10 has October's opal by month and Libra's opal by sign — those agree. Someone born on October 30 has October's opal by month but Scorpio's topaz by sign.

Neither is more authentic. The zodiac list is older; the monthly list is what jewelers use. The full zodiac version is here.

What the stone is actually made of

Every stone page in this reference carries its chemical composition, crystal system, Mohs hardness and where it is mined. That is deliberate: most birthstone writing online repeats the same handful of adjectives without a single verifiable fact, and it is impossible to tell one page from another.

The traditional associations are here too, but labeled as traditional. They are worth knowing as cultural history — they are not claims about what a mineral does.