August has three stones on the modern list, peridot, spinel and sardonyx, and two on the traditional list, peridot and sardonyx.
The two lists for August
Modern list (American Gem Society): Peridot, Spinel, Sardonyx
Traditional list (United Kingdom, National Association of Goldsmiths, 1937): Peridot, Sardonyx
There is no single official birthstone list, so you are free to choose whichever you prefer. You can check any month with our birthstone finder.
About the stones
Peridot
Peridot is the gem form of olivine, olive to lime green, with a hardness of 6.5 to 7. It is found in volcanic rock, in Arizona, Pakistan, Myanmar and on the Red Sea island once called Zabargad, and, rarely, in meteorites. Some writers have suggested that a number of the historic emeralds described in ancient texts were peridot, though that is debated.
Spinel
Spinel is a hard mineral with a hardness of 8, often red or pink, long mistaken for ruby. Myanmar, Sri Lanka and Tajikistan are well-known sources. It was added to the modern list more recently.
Sardonyx
Sardonyx is banded chalcedony with layers of brown-red sard and white onyx, used for carved cameos and seals in the Roman world. It is hardness 6.5 to 7.
How the idea developed
August is a clear case of a modern addition: spinel joined the American list comparatively recently, which shows the list is a living convention. The traditional United Kingdom list of 1937 holds only peridot and sardonyx, and the two lists together show how much variation is acceptable.
For the wider history of the idea, see our birthstones overview. The modern list follows the American Gem Society, and the traditional list follows the 1937 United Kingdom list, both summarised in Wikipedia, Birthstone.
A different system
Vedic gemstone (ratna) guidance is a different system from birthstones. It is tied to the nine planets and to a birth chart, not to the calendar month, and it belongs to the Vedic tradition, which is covered on our sister site, Nidarshana Vedh. Nothing on this page is Vedic advice.
A note on health. Crystals are valued for beauty, meaning and ritual. There is no scientific evidence that they treat health conditions. If you are struggling with your health or mood, please speak to a doctor.
Frequently asked questions
↳ Is spinel a new gem?
No. It is an old stone that was often mistaken for ruby. It was added to the modern birthstone list comparatively recently.
↳ Is peridot found in meteorites?
Yes, very rarely. Olivine occurs in some stony-iron meteorites, and a few have yielded gem-quality peridot.