Libra is the seventh sign of the Western zodiac, covering, in modern reckoning, the period from approximately 23 September to 22 October. As with all zodiac stone assignments, there is no single authoritative list; the tradition is composite, drawing on classical lapidary writing, on later astrological reworking, and on twentieth-century jewellery-trade promotion.

The most commonly cited Libra stones in the modern English-language tradition are opal and tourmaline, reflecting the October calendar overlap with that month's birthstones. Older astrological sources have associated the sign variously with sapphire, lapis lazuli, peridot and chrysolite. The Tibetan and Vedic systems use altogether different correspondences and should not be conflated with the Western list.

For working trade purposes the Libra association is a marketing rather than a gemmological category. There is no testable gemstone property that distinguishes a Libra stone from any other stone of the same species; the relationship is symbolic and traditional, and is best presented as such.