In the Western astrological tradition, Leo gems are the stones associated with the zodiac sign of Leo, conventionally the period from approximately 23 July to 22 August. The most consistent attribution across the modern lapidary literature is peridot, the August birthstone in the American Gem Society and Jewelers of America birthstone lists since the early twentieth century, and the principal stone marketed for Leo birthdays. Secondary attributions vary by source and tradition: ruby, sardonyx, golden topaz, citrine and yellow diamond all appear in different Leo lists, generally chosen for the colour symbolism (gold, sun) associated with the sign and its planetary ruler, the Sun.

The trade should be approached with two caveats. First, zodiac stones are a folk tradition with no laboratory or industry standard; lists vary between sources, eras and cultures, and the more prescriptive Vedic system uses different stones (typically ruby for Leo) on different planetary logic. Second, the modern birthstone lists themselves are commercial conventions adopted by trade associations, not ancient prescriptions. A buyer asking for a Leo gem is best served by being shown the conventional choices - peridot first, ruby and golden citrine as warm-toned alternatives - with the symbolic background explained rather than asserted as authoritative.