How Spinel and Sardonyx differ in what they are, color, hardness and care.
| Spinel | Sardonyx | |
|---|---|---|
| What it is | A hard, durable gem that is often mistaken for ruby or pink sapphire. Added as an August birthstone in 2016. | A banded chalcedony quartz with alternating layers of sard and onyx, used for jewelry, seals and cameos. |
| Birthstone for | August | August |
| Colors | Vivid red; Cobalt blue; Bright pink; Bright orange; Violet; Purple; Green; Brown; Gray; Black | Bands of reddish brown, cream, black and white; clean, well defined layers are valued most |
| Mohs hardness | 8 | 6.5 to 7 |
| Toughness | Good, which makes it a durable choice for jewelry. | Not stated |
| Everyday wear | Good for everyday wear | Wear with care |
| Ultrasonic cleaner | Usually safe (fractures can be a problem) | Not covered by AGS |
| Main sources | Myanmar (Burma), Sri Lanka, Tajikistan, Vietnam | India, Brazil, Uruguay, Germany |
| Common treatments | Some spinel is heat treated (stable). Fracture filling is rare. | Not stated |
Spinel is the harder of the two (8 on the Mohs scale). Both are August birthstones, so either makes a fitting gift. Choose by the color you love and how the piece will be worn; for a ring worn every day, the tougher stone will last better.
Sources: GIA: Spinel care and cleaning, AGS: Spinel, AGS: Sardonyx, AGS: Sardonyx. Checked October 16, 2026.
Birthstone of the month
On the first of each month: that month's birthstone, what it means and how to care for it.
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