August claims three official birthstones — more than any other month. Peridot, spinel, and sardonyx each bring a distinct character, from peridot's volcanic green to spinel's rainbow range to sardonyx's banded warmth.
Peridot: The Volcanic Gem
Peridot is the gem variety of olivine, a mineral that forms deep in the earth's mantle and arrives at the surface through volcanic eruptions. It's one of the few gemstones that exists in only one color: green. The shade ranges from yellow-green to olive to rich chartreuse, depending on iron content.
What makes peridot mineralogically fascinating is its origin story. Some peridot crystals arrive on earth inside meteorites — pallasites, specifically, which are stony-iron meteorites containing olivine crystals suspended in a nickel-iron matrix. These extraterrestrial peridots are among the rarest gemstones on earth.
The most important terrestrial source is the San Carlos Apache Reservation in Arizona, which produces about 80% of the world's commercial peridot. High-quality specimens also come from the Suppat Valley in Pakistan and Zabargad Island in Egypt's Red Sea — the original historic source, mined since 1500 BCE.
Peridot Facts
• Mohs hardness: 6.5-7
• Chemical formula: (Mg,Fe)₂SiO₄
• Crystal system: Orthorhombic
• The ancient Egyptians called it "the gem of the sun"
• Cleopatra's famous "emerald" collection was likely peridot
Spinel: The Underrated Gem
For centuries, the world's most famous "rubies" were actually spinels. The 170-carat Black Prince's Ruby in the British Imperial Crown? Spinel. The Timur Ruby, a 361-carat stone inscribed with the names of Mughal emperors? Also spinel.
Spinel was only added as an August birthstone in 2016 by the American Gem Trade Association, correcting centuries of underappreciation. This magnesium aluminum oxide (MgAl₂O₄) occurs in virtually every color: red, pink, blue, violet, orange, and black.
The most prized variety is "cobalt blue" spinel from Vietnam and Sri Lanka, which produces an intense, neon-like blue rivaling the finest sapphires. Red spinel from Myanmar's Mogok region and Tanzania's Mahenge deposits can rival ruby in color saturation at a fraction of the price.
Sardonyx: The Layered Stone
Sardonyx is a banded variety of chalcedony combining alternating layers of sard (reddish-brown) and onyx (white to black). It's been prized since antiquity for cameo carving — the contrasting layers allow artisans to carve raised white figures against dark backgrounds.
Roman soldiers wore sardonyx rings carved with Mars or Hercules into battle. The stone was believed to bestow courage and eloquence — a practical combination for military leaders who needed both.
Today, sardonyx is one of the most affordable semi-precious stones, making it an accessible entry point for August-born collectors. Quality specimens show sharp, well-defined bands with strong color contrast.
Collecting August Birthstones
Each of August's three birthstones offers a different collecting experience:
Peridot is best collected as faceted gems or raw crystal specimens. Large, clean peridot crystals from Pakistan are particularly stunning as display pieces.
Spinel is a gem collector's stone — undervalued relative to its beauty and rarity. Fine spinels in unusual colors (hot pink, cobalt blue, orange) are excellent investments.
Sardonyx shines as carved objects and vintage cameos. Estate jewelry featuring sardonyx cameos connects you to thousands of years of lapidary tradition.
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