August Birthstone: Peridot, Spinel or Sardonyx, Which One?

Start from the color you want on your hand.

• Choose peridot for green, from lime to olive. It never comes in another color, because iron is part of the mineral itself. It is the most affordable untreated green stone in standard sizes.
• Choose spinel for red, pink, orange, violet or blue. The finest reds can rival ruby, and the stone is hard and tough enough for daily wear in any jewel.
• Choose sardonyx for straight bands of reddish brown with white or black. It is carved into cameos and seals, and cut into beads and cabochons, often in large sizes.

Spinel, clearly. It rates 8 for hardness and good for toughness, so it suits any jewel worn every day, rings included. Peridot and sardonyx both rate 6.5 to 7: sardonyx is tough, while peridot scratches more easily and is only fair to good against knocks.

So a peridot ring wants a setting that guards its edges, and it is happier in a pendant or earrings. Two habits for peridot: tell your jeweler before any resizing, because a sudden temperature change can crack it, and clean it in warm soapy water, never with steam, and skip the ultrasonic. Spinel and sardonyx usually tolerate an ultrasonic cleaner. More in our guide to peridot jewelry.

Sardonyx and peridot are the affordable two. Spinel is the one whose price climbs, with its color.

• Sardonyx is plentiful and inexpensive, even in large pieces.
• Peridot is inexpensive in small sizes; prices rise above about 10 by 8 millimeters, and the finest large stones come from Myanmar and Pakistan.
• Spinel is priced by color: lavender and violet sell for less, then vivid orange and hot pink, then cobalt blue, and red is the most valued. Fine red, pink and blue stones over 5 carats get scarce, and dear.

What sellers asked on 18 October 2026, in the listings we read: faceted peridot of 4 to 7 carats, $70 to $360 a carat, the spread between the median prices of three sellers. Next to ruby, spinel stays reasonable: a top red spinel of 5 carats might sell for around a tenth of an equivalent ruby. For spinel by color, see our spinel price guide; for the wider market, our colored gemstone market statistics.

Treatment is rarely the problem here. Imitation is.

• Peridot has no known treatment. But glass and synthetic spinel imitate it, and synthetic spinel is common in birthstone jewelry.
• Spinel is rarely treated. Because the synthetic is so common, many people have never seen a natural one.
• Sardonyx belongs to chalcedony, a family that is commonly dyed.

In the US, an imitation cannot be sold as a birthstone under the gem's name alone: the word imitation or simulant must appear just as clearly. Look for it on the label.

One clue for peridot: it splits light so strongly that the back facet edges can look doubled, sometimes without a loupe. Seeing it rules out glass and synthetic spinel, which never double; not seeing it proves nothing. Ask for a report from an independent laboratory that names the species and says natural or synthetic: what a lab report proves.