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August Birthstone: Peridot, Spinel, and Sardonyx
August is one of three months — alongside June and December — assigned more than one birthstone. Peridot, spinel, and sardonyx arrived at that position by three different routes: one long-standing, one recently formalized, one older than any official list. Each has its own mineral family, its own colour behaviour, and its own case for or against daily wear. This guide works through what each stone actually is, why August ended up with three, and what that means for anyone choosing one for an engagement ring or a fine jewelry piece.
Table of Contents
What Is the Birthstone for August?
August carries three recognized birthstones: peridot, spinel, and sardonyx. Peridot is the long-standing modern stone, holding the August position since the National Association of Jewelers formalized the first modern birthstone list in 1912. Spinel is the most recent addition, given official status in 2016 by the American Gem Trade Association and Jewelers of America. Sardonyx is the oldest of the three by association, tied to August in tradition long before any standardized list existed.
None of the three outranks the others today — each simply carries a different kind of claim. Peridot by tenure on the modern list, spinel by recent formal recognition, sardonyx by history.
Why Does August Have Three Birthstones?
August, June, and December are the only three months with more than one recognized birthstone—the result of a list assembled and revised across more than a century, not a single decision. Peridot has occupied the August position since 1912. Sardonyx predates that list, carried forward from a much older tradition tied to Roman and Renaissance use. Spinel is the newest arrival, added in 2016 largely to give the stone standing of its own, after centuries spent mistaken for ruby in some of history’s most famous jewels.
The practical effect is a birth month spanning a volcanic green gem formed deep in the earth’s mantle, a stone whose finest reds fooled European royalty for hundreds of years, and a banded quartz carved into seal rings since antiquity. Three stones, three mineral families, three separate design conversations.
What Is the Colour for an August Birthday?
There is no single colour for August. Peridot is consistently green — coloured by iron within its own crystal structure, which means it does not occur in other hues the way sapphire or spinel do. Spinel spans the widest range of the three: vivid red, pink, orange, purple, violet, and blue, with fine red and pink stones coloured by the same chromium responsible for ruby’s colour. Sardonyx is banded rather than uniform — alternating layers of reddish-brown sard and white or cream onyx.
If one colour is associated with August by default, it is peridot’s green, the most consistently visible of the three in the current market. But the accurate answer is that August spans green, a near-complete spectrum of red through blue, and a banded brown-and-white pattern rather than holding to one hue.
Peridot: Structure and Meaning
Peridot is the gem variety of olivine, coloured green by iron built into its own crystal structure rather than by a trace impurity. That structural link is why peridot occurs in essentially one colour family — a consistent grass green — regardless of where it was mined, unlike gems whose colour shifts by trace element or origin.
Formation sets peridot apart from almost every other gemstone: it forms deep within the earth’s mantle and reaches the surface through volcanic activity, one of the few gems, alongside diamond, that originates at that depth. Peridot has also been recovered from pallasite meteorites — one of a small number of gem materials with a documented extraterrestrial source.
Historic supply came from Zabargad Island in the Red Sea, mined by ancient Egypt under the name Topazios as early as the third century BCE. Modern sources include Myanmar’s Kyaukpon region, Pakistan’s Kashmir Valley — known for an especially saturated, pure green — and Arizona’s San Carlos Apache Indian Reservation, the largest current source by volume, alongside material from China, Vietnam, and Tanzania. Ancient Egyptian priests wore peridot as early as the second century BCE, and historians have suggested that Cleopatra’s celebrated “emeralds” were in fact peridot. For the authoritative reference on formation, sourcing, and grading, GIA’s peridot resource is the industry standard.
Structurally, peridot ranks 6.5 to 7 on the Mohs scale — moderate hardness, but with distinct cleavage in one direction that makes it more prone to chipping at facet edges than the hardness number alone suggests.
On peridot’s green: Because iron is part of the crystal itself rather than a trace addition, peridot cannot be treated or heated to change its colour the way many gemstones can. What you see in a peridot is the stone’s structure, not a modification of it.
Spinel: Structure and Meaning
Spinel is a distinct mineral — magnesium aluminum oxide — with no structural relationship to ruby or sapphire despite a long history of being mistaken for both. It occurs across the widest colour range of the three August birthstones: intense red, vibrant pink, orange, purple, violet, and blue. Chromium produces spinel’s finest reds and pinks, the same trace element responsible for ruby’s colour, which is precisely why the two were confused for centuries.
That confusion shaped some of history’s most famous jewels. The Black Prince’s Ruby, roughly 170 carats and set in Britain’s Imperial State Crown above the Cullinan II diamond, is in fact a red spinel — worn by English monarchs since Edward, Prince of Wales acquired it in 1367. The Timur Ruby, a 361-carat stone inscribed by Mughal emperors and later part of the British Crown Jewels, is likewise a red spinel. Reliable chemical differentiation between spinel and corundum only became possible in the 18th century. For grading standards and sourcing detail, GIA’s spinel resource is the reference point.
Spinel’s formal recognition as an August birthstone is recent: the American Gem Trade Association and Jewelers of America added it in 2016, giving the stone standing of its own after centuries in ruby’s shadow.
Structurally, spinel is the most durable of the three August birthstones — 8 on the Mohs scale, with excellent toughness and no cleavage. Major sources include Myanmar’s Mogok Stone Tract, the same region that produces fine ruby, alongside Tajikistan, Sri Lanka, Vietnam’s Luc Yen region, and Tanzania.
On spinel and ruby: Spinel and ruby can share a strikingly similar red, but they are unrelated minerals. A red spinel is not a lesser ruby or a substitute for one — it is its own gemstone, with its own hardness, its own sourcing, and, since 2016, its own place on the birthstone calendar.
Sardonyx: Structure and Meaning
Sardonyx is a banded variety of chalcedony, a cryptocrystalline form of quartz, formed from alternating layers of sard — a warm reddish-brown — and onyx, its white or cream counterpart. The banding is the entire identity of the stone: where the layers run straight and distinct, sardonyx becomes the material of choice for carving a design in one colour against a contrasting ground.
That property made sardonyx the standard material for engraved seal rings across the ancient world. Greek and Roman engravers carved intaglios — designs cut into the stone — and cameos — designs raised in relief — using the banding to separate a figure from its background in a single piece of material. The finished rings were worn daily and pressed into wax to seal documents, which meant the stone needed to survive constant handling, not sit in a vitrine. Sardonyx’s fine-grained, fibrous structure gives it good toughness and no cleavage despite a modest hardness, which is exactly the property that let it function for that purpose for thousands of years. The tradition continued through the Renaissance, when sardonyx remained a preferred material for carved cameos and decorative seals.
Major sources include India, historically the most significant supplier, along with Brazil, Uruguay, and Germany — Idar-Oberstein has been a centre for sardonyx cutting and carving for generations — plus smaller deposits in the western United States.
Structurally, sardonyx ranks 6.5 to 7 on the Mohs scale, the same nominal hardness as peridot, but its microcrystalline structure gives it meaningfully better resistance to chipping — the distinguishing factor between a stone graded by hardness number alone and one graded by how it actually performs in use.
On banding: No two pieces of sardonyx carry identical banding. For a carved or cameo piece, the width, contrast, and straightness of the layers determine what the material can be cut into — the design follows the stone, not the other way around.
Continuing the birthstone series: Read our guide to July’s birthstone → July Birthstone: Ruby
Choosing an August Birthstone for an Engagement Ring
Of the three, spinel is the only one structurally comparable to ruby or sapphire as an everyday engagement ring centre stone. At 8 on the Mohs scale with excellent toughness and no cleavage, it holds up to daily wear without the setting compromises softer stones require, while offering a colour range — from deep red to violet-blue — that a single-colour stone cannot match.
Sardonyx is durable in its own right, its toughness proven over millennia of daily-worn seal rings, but its opaque, banded character reads as a graphic design element rather than a brilliant centre stone. It suits a low-profile or bezel setting built around the banding itself, more than a conventional solitaire.
Peridot is the most fragile of the three for ring use. Its cleavage means a real chance of chipping at the facet edges from the kind of daily knocks a ring absorbs, so it performs better in earrings, pendants, or, if used as a ring stone at all, a protective setting that limits contact at the edges.
At Lumi, that structural read happens in CAD before any stone is set. Proportion, the angle of light entry, how the stone sits against the hand, and the protection a particular stone requires are worked through on screen and confirmed before production begins. An August birthstone ring — in any of the three stones — is built around what that stone specifically requires, not a template applied regardless of material.
Care and Maintenance
Peridot — Clean only with warm, soapy water and a soft brush. Its cleavage and sensitivity to sudden temperature change make ultrasonic and steam cleaning unsafe, and either can cause a fracture along the cleavage plane.
Spinel — Clean with warm, soapy water. Given its hardness and excellent toughness, ultrasonic and steam cleaning are generally safe, though warm soapy water remains the more conservative option for coloured stones overall.
Sardonyx — Clean with warm, soapy water and a soft cloth. Avoid harsh chemicals and prolonged heat exposure, which can dull the polish across the banded layers over time.
