Most months make do with one birthstone. August gets three, and none of them is a consolation prize. Peridot is one of the only gems that occurs in a single colour, formed deep in the earth's mantle and carried to the surface by volcanic activity. Spinel spent centuries being mistaken for ruby, including in a set of crown jewels. Sardonyx is the oldest of the three, the banded stone Roman officials pressed into wax to seal their letters.
If you were born in August, or you're buying for someone who was, the useful question isn't which stone is best. It's which one suits the way the jewelry will actually be worn. Here's how each behaves, what separates a fine example from an ordinary one, and how they compare when it comes to daily wear.
Why August has three birthstones
Sardonyx is the traditional choice, carried down from antiquity. Peridot joined it on the modern list drawn up by American jewellers in 1912 and has been the month's most recognised stone ever since. Spinel is the newcomer: in 2016, Jewelers of America and the American Gem Trade Association added it, correcting a long-standing oversight for a gem the trade had admired for decades. You can see how the full calendar fits together on our birthstone guide by month.
Three official stones is a genuine advantage. It means an August birthday can be marked in vivid grass green, in a red that rivals fine ruby, or in warm carved bands of orange-brown and white, depending on taste, budget and how hard the piece has to work.
Peridot: green with nowhere to hide
Peridot is the gem-quality variety of olivine, and it is idiochromatic, meaning its colour comes from iron built into the crystal structure itself rather than from trace impurities that happen to wander in. That single fact explains a great deal about the stone. There is no colourless peridot, no blue peridot, no pink peridot. Every specimen sits somewhere on a narrow band between yellowish green and greenish yellow, and the only real variable is how far it leans.
What separates a fine peridot
The most prized colour is a rich, saturated grass green with as little brown or yellow drift as possible. Because iron content drives both colour and saturation, larger peridots tend to show deeper colour than small ones. A well-cut two- or three-carat stone will often read considerably greener than a half-carat from the same parcel, which is why melee-sized peridot can look washed out next to a single statement stone.
Clarity expectations are high. Fine peridot is typically eye-clean, and the classic inclusion to look for under magnification is the "lily pad": a small chromite crystal surrounded by a flat, disc-shaped stress fracture. It is a charming diagnostic feature rather than a flaw to fear, and its presence is good evidence you're looking at natural material.
Cut deserves attention too. Peridot has strong double refraction, and if you look through the table with a loupe you can usually see the back facet edges appear doubled. A cutter who ignores this can produce a stone that looks slightly soft or blurred face-up; a good one orients the rough so the doubling stays discreet and the stone returns light cleanly.
Seeing stones together like this is the fastest way to train your eye. Colour is comparative: a peridot that looks superb on its own can lose its nerve beside a livelier neighbour, and one that seemed unremarkable can turn out to be the cleanest of the group. When you browse our loose peridots, compare a few side by side before settling.
Where peridot comes from
Fine material comes from the high-altitude deposits of Pakistan's Kohistan region, from Myanmar, from China and Vietnam, and from the San Carlos Apache Reservation in Arizona, which has supplied American peridot for generations. Historically, the source that mattered most was Zabargad, a small island in the Red Sea worked for thousands of years; the Egyptians called peridot the gem of the sun. The large green stones in the Shrine of the Three Kings at Cologne Cathedral were believed to be emeralds for centuries before being identified as peridot. Peridot is also, uniquely, found in pallasite meteorites, which makes it one of the very few gems you can buy with an extraterrestrial pedigree.
Living with peridot
This is where honesty matters. Peridot sits at 6.5 to 7 on the Mohs scale, has imperfect cleavage and is somewhat brittle. It also dislikes sudden temperature changes and is vulnerable to acids, including, over time, the ones in perspiration and household cleaners. None of this makes it a bad gem, but it does make it a thoughtful one.
In earrings and pendants, peridot is essentially trouble-free. In a ring worn every day, it needs help: a bezel or a low, protective setting rather than high claws that leave the girdle exposed. Clean it with warm water, mild soap and a soft brush, and keep it away from ultrasonic and steam cleaners entirely.
Trying a loose stone against the hand before committing is worth the extra step. It shows you how the proportions read on a real finger, how the colour behaves against skin, and whether the shape wants a protective mount. If you're planning something specific, our bespoke service starts with exactly this conversation.
Spinel: the gem that fooled kings
Spinel has the strangest reputation in the gem world: for most of recorded history, nobody knew it existed as a separate species. Red spinel from central Asia was sold as "balas ruby" and set into royal jewels across Europe and the Middle East. Two of the most famous "rubies" in the British Crown Jewels, the Black Prince's Ruby and the Timur Ruby, are spinels. Only in the eighteenth and nineteenth centuries did chemistry settle the matter.
Colour, and why the trade pays attention
Spinel is magnesium aluminium oxide, it crystallises in the cubic system, and it is singly refractive. That last point has a practical consequence: no double refraction to blur the back facets, so a well-cut spinel has a crisp, clean brilliance. It reaches 8 on the Mohs scale with no troublesome cleavage, which makes it markedly more suitable for everyday rings than peridot.
The colour range is enormous: vivid reds that stand comparison with ruby, hot pinks, lavenders and violets, orange-reds, greys, and the rarest of all, the cobalt-coloured blues from Vietnam and Sri Lanka, where cobalt rather than iron does the work. Mogok in Myanmar has produced fine red and pink spinel for centuries. Tanzania's Mahenge deposit caused a stir in the trade when it began producing intensely saturated, almost neon pinks and reds. Vietnam's Luc Yen region supplies both pastel and cobalt material.
The other quiet virtue is that spinel is very rarely treated. In a market where heat treatment is routine for sapphire and ruby, and clarity enhancement is standard practice for emerald, an untreated natural gem with excellent hardness and top-tier colour is unusual. That combination is why serious collectors have been buying spinel for years, and why our spinel collection tends to move quickly.
Sardonyx: the original August birthstone
Sardonyx is a banded variety of chalcedony, a cryptocrystalline quartz, formed of alternating layers of sard, which ranges from brownish red to warm orange-brown, and onyx, which is typically white or black. At 6.5 to 7 on the Mohs scale it is comparable to peridot in hardness, but because it has no cleavage and a compact microcrystalline structure, it is considerably tougher in practice.
Those parallel bands are the whole point. Roman carvers used them to cut cameos and intaglios in which a pale figure stands out against a dark ground, and sardonyx signet rings were used to seal documents precisely because hot wax doesn't stick to a polished stone. If you want an August birthstone with genuine antiquity behind it, this is the one. A note on disclosure: chalcedony is commonly dyed to intensify or standardise its banding, so ask, and expect a straight answer.
Choosing between the three
A rough guide. If you want unmistakable, joyful green and the piece will be a pendant, a pair of earrings or an occasional ring, choose peridot. If it's an engagement ring or something worn daily on the hand, choose spinel: the hardness, the toughness and the near-absence of treatment make it the practical answer, and the colour range means you're not limited to red. If you're drawn to carving, warm earth tones or historical pieces, sardonyx is the interesting choice and the most affordable entry to the month.
You can see the loose stones we currently hold in the August birthstone collection, and finished pieces in August birthstone jewelry. Because loose coloured stones are one of a kind, availability shifts constantly.
Buying an August birthstone with confidence
Three habits will protect you. First, ask what the stone is, in species terms, and how that was established. Peridot's refractive index of roughly 1.654 to 1.690 and its strong birefringence distinguish it immediately from green glass, green sapphire or emerald; spinel's single refraction separates it from ruby in seconds under a refractometer. Any competent gemologist can confirm both.
Second, ask about treatment, and get it in writing. Peridot is one of the few gems that is almost never enhanced, spinel is usually untreated, and sardonyx is frequently dyed. A seller who is vague about this is telling you something.
Third, for anything significant, ask for an independent laboratory report. It costs relatively little against the value of a good stone and it removes the guesswork from identification, origin and treatment. If you're looking for something we don't currently have in stock, tell us what you're after and we'll go and find it.
Frequently Asked Questions
What is the birthstone for August?
August has three official birthstones: peridot, spinel and sardonyx. Sardonyx is the traditional stone inherited from antiquity, peridot was included on the modern American list established in 1912, and spinel was added in 2016 by Jewelers of America and the American Gem Trade Association. Peridot is the one most people picture, but all three are equally correct. Which you choose usually comes down to colour preference and how the piece will be worn. You can see what we currently hold in our August birthstone collection.
Is peridot durable enough for an engagement ring?
Peridot can work in an engagement ring, but it needs the right setting. At 6.5 to 7 on the Mohs scale with imperfect cleavage and some brittleness, it is softer and more vulnerable than sapphire or spinel, and an exposed girdle in a high claw setting will eventually chip. A bezel or a low, protected mount changes the equation considerably. If the ring will be worn every single day without removal, spinel at Mohs 8 is the more practical August stone. We're happy to talk through both options before you commit.
How can you tell if a peridot is real?
The most reliable everyday clue is doubling. Peridot has strong double refraction, so looking through the table with a loupe usually reveals the back facet edges appearing as two lines rather than one. Green glass and green cubic zirconia show no doubling, and emerald's doubling is far weaker. A refractometer settles it outright, since peridot reads roughly 1.654 to 1.690. Natural stones often also show the distinctive lily pad inclusion, a small crystal ringed by a flat disc-shaped fracture. For anything valuable, an independent laboratory report is worth the cost.
Why is spinel considered special among the August birthstones?
Spinel combines qualities that rarely appear together. It reaches 8 on the Mohs scale with no problematic cleavage, so it handles daily wear well. It is singly refractive, which gives well-cut stones a crisp brilliance. Its colour range runs from vivid red and hot pink through lavender to rare cobalt blue. Most importantly, spinel is very seldom treated, which is unusual in a market where heat treatment and clarity enhancement are routine for other coloured stones. For decades it was mistaken for ruby, including in the British Crown Jewels.
How do you clean and care for peridot jewelry?
Warm water, a mild soap and a soft brush, then rinse and pat dry. Never use an ultrasonic or steam cleaner on peridot, as both risk damage from vibration and thermal shock. Peridot is sensitive to sudden temperature changes and to acids, so remove it before swimming, cleaning or applying perfume and hairspray. Store it separately from harder gems such as sapphire, spinel or diamond, which will scratch it in a shared jewelry box. Have the setting checked periodically if the piece is worn often.
Are August birthstones treated or enhanced?
It varies sharply by stone. Peridot is one of the very few gems that is almost never treated, so what you see is essentially what came out of the ground. Spinel is usually untreated as well, which is part of its appeal to collectors. Sardonyx is the exception: like other chalcedonies it is frequently dyed to intensify or even out its banding, and that should always be disclosed. Whichever you buy, ask for treatment disclosure in writing, and request an independent laboratory report for any significant purchase.
