August Birthstone: Peridot, Sardonyx & Spinel
August claims three birthstones — peridot, sardonyx, and spinel — joining June and December as the months with the most. Sardonyx served as the original August birthstone for centuries before peridot joined the list in 1912, and spinel followed in 2016. Each stone carries a distinct history in antique jewellery, from Egyptian peridot mines to Roman sardonyx intaglios and the red spinels that masqueraded as rubies in European crown jewels. All three stand at 6.5 or above on the Mohs hardness scale, making each suitable for jewellery wear. This guide covers all three August birthstones, their gemmological properties, and how they appear in antique rings.
What Is the August Birthstone?
August has three recognised birthstones: peridot, sardonyx, and spinel. Peridot — a vivid yellow-green gemstone formed deep in the Earth's mantle — is the primary modern birthstone. Sardonyx, a banded variety of chalcedony, is the traditional stone dating to antiquity. Spinel, a magnesium aluminium oxide prized for its range of vivid colours, was added in 2016.
The modern birthstone list was standardised in August 1912 by the American National Association of Jewelers (now Jewelers of America) at their convention in Kansas City. That list assigned peridot as August's primary birthstone, replacing sardonyx in the featured position. The connection between gemstones and calendar months dates to at least the first century, when the historian Josephus drew parallels between the twelve stones of the High Priest's breastplate and the twelve months. The list has been revised sparingly since 1912 — alexandrite, citrine, and pink tourmaline were added in 1952, tanzanite joined December in 2002, and spinel was added to August in June 2016 by the American Gem Trade Association and Jewelers of America.
| Stone | Status | Mohs Hardness | Chemical Formula | Colour Range |
|---|---|---|---|---|
| Peridot | Primary modern (1912) | 6.5–7 | (Mg,Fe)₂SiO₄ | Yellow-green to olive green |
| Sardonyx | Traditional (antiquity) | 6.5–7 | SiO₂ | Banded red-brown and white |
| Spinel | Added 2016 | 8 | MgAl₂O₄ | Red, pink, blue, purple, orange |
What Is Peridot and Where Does It Come From?
Peridot is a gem-quality variety of the mineral olivine, with the chemical formula (Mg,Fe)₂SiO₄. It forms in the Earth's upper mantle and reaches the surface through volcanic activity. Peridot ranks 6.5 to 7 on the Mohs hardness scale and displays a colour range from yellow-green to deep olive green, with traces of iron producing the characteristic hue.
The ancient Egyptian island of Zabargad (also called St John's Island) in the Red Sea was the world's principal peridot source for over two thousand years. Archaeological evidence from the ancient port of Berenice confirms mining on Zabargad from the third century BC. The Egyptians called peridot 'the gem of the sun' and mined it under harsh conditions — ancient sources record that miners worked at night, believing the stones were easier to spot after dark.
One of peridot's most distinctive optical properties is its strong birefringence — a doubling effect visible under magnification, where the rear facet edges appear as two parallel lines. This characteristic, with a birefringence value of 0.035 to 0.038, distinguishes peridot from emerald, garnet, and other green gemstones at a glance through a jeweller's loupe.
Why Was Peridot Confused with Emerald?
Peridot and emerald share a green appearance that led to centuries of misidentification. The large peridots adorning the Shrine of the Three Holy Kings in Cologne Cathedral were long believed to be emeralds until gemmological analysis proved otherwise. Several scholars have argued that Cleopatra's famed emerald collection included peridots from nearby Red Sea mines.
The confusion stems from the overlapping sources of both minerals. Zabargad, the primary peridot mine, was known in antiquity as Topazios — a name later transferred to an entirely different mineral. Ancient writers used the terms topazos, smaragdos (emerald), and chrysolite (an old name for peridot) interchangeably, and traders rarely distinguished between green stones of similar hue. The Red Sea island sat close to Egyptian emerald mines in the Eastern Desert, and goods from both sources passed through the same trading ports.
Modern gemmology separates the two instantly. Peridot's strong double refraction — absent in emerald — provides a decisive visual test under magnification. Visit the A-Z of Gemstones reference for detailed profiles of peridot and other stones found in antique jewellery.
| Property | Peridot | Emerald |
|---|---|---|
| Mohs hardness | 6.5–7 | 7.5–8 |
| Refractive index | 1.654–1.690 | 1.577–1.583 |
| Double refraction | Strong (0.035–0.038) | Weak (0.005–0.009) |
| Colour tone | Yellow-green | Blue-green |
What Is Sardonyx and Why Was It the Original August Birthstone?
Sardonyx is a banded variety of chalcedony — a microcrystalline form of quartz — composed of alternating layers of sard (brownish-red) and onyx (white or black). It ranks 6.5 to 7 on the Mohs hardness scale with the chemical formula SiO₂. Sardonyx held the position of August birthstone from antiquity until 1912, when peridot replaced it on the modern list.
Roman soldiers carved images of Mars, the god of war, into sardonyx rings and wore them into battle as talismans of courage and protection. The stone's layered structure made it ideal for glyptic art — the contrasting bands of brown-red and white allowed carvers to create detailed cameos and intaglios with natural colour contrast, and hot wax would not stick to the polished surface, making sardonyx the preferred material for seal rings.
Victorian jewellers continued the tradition. Sardonyx appeared in mourning rings, signet rings, and carved cameo pieces throughout the nineteenth century. The stone's sombre tones and association with classical antiquity suited Victorian taste, and the ease with which it could be carved into profile portraits and floral designs kept it in steady demand through the entire period.
Why Was Spinel Added as an August Birthstone?
The American Gem Trade Association and Jewelers of America announced spinel as an official August birthstone in June 2016. It was only the third update to the modern birthstone list in over a century. The addition recognised spinel's gemmological credentials — a Mohs hardness of 8 and a colour range spanning red, pink, blue, purple, and orange.
Spinel's chemical formula is MgAl₂O₄ — magnesium aluminium oxide. Its similarity to ruby (aluminium oxide, Al₂O₃) caused centuries of misidentification. The International Colored Gemstone Association has called spinel 'the great impostor of gemstone history' because several celebrated crown jewel 'rubies' are spinels. Mineralogists could not reliably distinguish the two until chemical analysis methods developed in the late eighteenth century. Today, spinel is recognised as a distinct mineral, with principal sources including Myanmar's Mogok Valley, Sri Lanka, and Tanzania. Red and pink spinels from Myanmar remain the most sought after, while cobalt-blue specimens from Sri Lanka and vivid neon-pink stones from Tanzania's Mahenge district have attracted growing collector interest.
| Name | Weight | Location | Notes |
|---|---|---|---|
| Black Prince's Ruby | ~170 ct | Imperial State Crown, England | Uncut red spinel; acquired c. 1367 |
| Timur Ruby | 361 ct | Royal Collection, England | Presented to Queen Victoria, 1851 |
| Catherine the Great's Ruby | ~398 ct | Imperial Crown of Russia | Commissioned 1763 |
How Do August Birthstones Appear in Antique Jewellery?
Peridot appears most frequently in Edwardian jewellery, particularly in the green-white-violet colour combination associated with the suffragette movement. Sardonyx features in Victorian signet rings, mourning jewellery, and carved cameos dating from the Roman period onwards. Spinel, though historically misidentified as ruby, can be found in Victorian and earlier pieces once classified as containing rubies.
Edwardian jewellers combined peridot with amethyst and pearl to create pieces in the suffragette colours of green, white, and violet — said to stand for 'Give Women Votes'. The London jeweller Mappin & Webb produced a catalogue of suffragette jewellery for Christmas 1908, and the combination became popular in pendants, brooches, and rings. Not every Edwardian piece in these colours was made with political intent, but the association has made peridot-amethyst-pearl pieces highly collectible.
Sardonyx's role in antique rings centres on its use as a carving medium. The layered structure — dark sard against white onyx — provided natural contrast for portrait cameos and heraldic intaglios. Browse our collection of antique agate rings to see examples of carved chalcedony in antique settings, or explore our wider gemstone ring collection for peridot and other coloured stone pieces.
Frequently Asked Questions
Is peridot durable enough for daily wear in a ring?
Peridot scores 6.5 to 7 on the Mohs hardness scale — softer than sapphire (9) or diamond (10) but comparable to garnet and quartz. It can be worn daily in a protective setting such as a bezel or cluster, but it requires more care than harder stones. Avoid ultrasonic cleaners and harsh chemicals; warm soapy water and a soft brush are the safest cleaning method. In antique rings, peridot settings often feature closed-back or collet mounts that shield the stone from lateral impact. These older settings provide better protection than modern open-back claw mounts, but the metal around the stone should be checked periodically for wear, as Victorian and Edwardian collets can thin over a century of use, loosening the stone in its seat.
How can you tell peridot from emerald?
Examine the stone under magnification for doubling — peridot's strong birefringence causes the back facet edges to appear as parallel double lines, an effect absent in emerald. Peridot also displays a warmer, more yellow-toned green, while emerald tends towards a cooler, bluer green. A gemmologist can confirm identification through refractive index testing: peridot reads 1.654–1.690 versus emerald's 1.577–1.583.
What is the most valuable of the three August birthstones?
Spinel commands the highest prices per carat among the three August birthstones. Fine red spinels from Myanmar's Mogok Valley rival ruby in colour intensity and exceed it in clarity, with top specimens selling for significant sums at auction. Peridot is more affordable, with fine stones available at a fraction of spinel's price. Sardonyx remains the most accessible, valued primarily for its carving quality rather than per-carat weight. Well-carved Victorian sardonyx cameos hold their value based on artistry and condition.
Where does the name "peridot" come from?
The etymology is debated. Some scholars trace it to the Arabic word faridat, meaning 'gem'. Others link it to the Old French peritot, meaning 'unclear' — a possible reference to cloudy lower-quality specimens. The ancient Greek name for the Zabargad mining island, Topazios, led to peridot being called 'topaz' in antiquity, adding to centuries of naming confusion among green and yellow gemstones.
Are old spinels in antique jewellery labelled as rubies?
Many antique pieces containing red spinel were sold and catalogued as ruby before modern mineralogical testing became available. If you own a Victorian or earlier ring described as ruby, a qualified gemmological laboratory can determine whether the stone is true corundum or spinel. Both are valuable — the identification matters for accurate documentation rather than diminishing the piece's worth or desirability. In some cases, confirmed spinel provenance from historic sources like the Badakhshan mines adds its own premium among specialist collectors.
Related Reading
- Gemstone Symbolism: What Stones Really Mean — the history and meaning behind precious stones in antique jewellery
- What Is Suffragette Jewellery? — the story behind the green, white, and violet jewellery of the Edwardian era
- Garnets: The Traveller's Stone — another coloured gemstone with deep roots in antique ring design
- Explore our complete guide to gemstones in antique rings — the Gemstones pillar page