Peridot, the vibrant green gemstone cherished for millennia, holds a unique position in the world of birthstones. As the traditional birthstone for August, it is celebrated for its distinctive olive-to-lime green hue, a color attributed to its iron content. Unlike many gemstones, peridot is formed deep within the Earth's mantle and brought to the surface through volcanic activity, making it one of the few gemstones found in extraterrestrial meteorites. This article explores the rich history, geological origins, gemological properties, and cultural significance of peridot, drawing on authoritative sources to provide a detailed portrait of this captivating gem.
History and Lore
The history of peridot stretches back to ancient civilizations, where it was often mistaken for other green gemstones due to limited gemological knowledge. One of the most significant historical sources for peridot is the island of Zabargad (also known as St. John’s Island) in the Red Sea. For over 3,500 years, this location was the primary source of peridot, with mining operations dating back to the Pharaonic period in ancient Egypt. The Egyptians referred to peridot as the "gem of the sun" and believed it possessed protective powers against evil spirits and night terrors. It was often set in gold and worn as amulets.
During the Middle Ages, peridot continued to be highly valued, particularly by the clergy. It was often confused with emerald, and many historical "emeralds" in church treasures have been re-identified as peridot. The most famous example is the large peridot gem in the shrine of the Three Kings at Cologne Cathedral, which was originally believed to be an emerald. The gem's journey to becoming a modern birthstone was formalized in 1912 by the American National Association of Jewelers (now Jewelers of America), which established a standardized list of birthstones. Peridot was designated for August, a tradition that continues to this day. Historical accounts from various eras highlight its use in royal jewelry and religious artifacts, underscoring its enduring appeal.
Geological Formation and Sources
Peridot is a variety of the mineral olivine, with the chemical formula (Mg, Fe)₂SiO₄. Its formation is unique among gemstones. Unlike gems that crystallize in the Earth's crust, peridot forms in the Earth's mantle under extreme heat and pressure. It is brought to the surface primarily through volcanic activity, often found in basaltic lava flows. This deep-earth origin explains why peridot crystals are sometimes found in volcanic rocks and even in certain meteorites, most notably pallasite meteorites, which contain peridot crystals embedded in a metallic matrix.
The primary commercial sources of peridot have historically been from the Red Sea, specifically the island of Zabargad. However, significant deposits have also been found in other locations. In the United States, peridot is found in Arizona, particularly in the San Carlos Apache Reservation, which is a major source of gem-quality material. Other notable sources include Pakistan, Myanmar (Burma), China, and Australia. The gem's color is directly influenced by its iron content; higher iron levels result in a more intense yellowish-green, while lower iron yields a purer green. The most valued peridot exhibits a rich, vibrant olive green without brownish overtones.
Gemological Properties
Peridot possesses a distinct set of gemological characteristics that differentiate it from other green gemstones like emerald or tourmaline. Its properties are consistent and make it a durable choice for jewelry, though it requires proper care.
- Chemical Composition: (Mg, Fe)₂SiO₄, a solid solution series between forsterite (Mg₂SiO₄) and fayalite (Fe₂SiO₄).
- Crystal System: Orthorhombic.
- Hardness: 6.5 to 7 on the Mohs scale. This makes it relatively durable for everyday wear, though it is softer than sapphire or diamond and can be scratched by materials with a higher hardness.
- Specific Gravity: 3.27 to 4.37, with a typical range around 3.34.
- Refractive Index: 1.654 to 1.690, with a birefringence of 0.036.
- Pleochroism: Weak to distinct, showing different shades of green and yellow-green when viewed from different crystal directions.
- Inclusions: Peridot often contains inclusions that are characteristic of its formation. Common inclusions include small, disc-shaped "lily pad" inclusions, needle-like crystals, and fluid inclusions. Unlike emerald, peridot is typically not treated, and its inclusions are often accepted as part of its natural beauty.
- Color: The color range for peridot is from yellowish-green to olive green. The most prized color is a pure, saturated green without brown or yellow overtones. The presence of iron (Fe²⁺) is responsible for the green color, while traces of other elements can affect the hue.
The following table summarizes key gemological properties of peridot:
| Property | Specification |
|---|---|
| Mineral Species | Olivine |
| Chemical Formula | (Mg, Fe)₂SiO₄ |
| Hardness (Mohs) | 6.5 - 7 |
| Crystal System | Orthorhombic |
| Refractive Index | 1.654 - 1.690 |
| Specific Gravity | 3.27 - 4.37 (typically ~3.34) |
| Typical Inclusions | "Lily pad" inclusions, needles, fluid inclusions |
| Common Treatments | Generally none (unheated) |
Symbolism and Metaphysical Beliefs
Peridot's symbolism is deeply rooted in its historical associations with the sun and protection. In ancient Egypt, it was believed to be a gift from the sun god Ra, and wearing it was thought to ward off evil and bring happiness and peace. The stone was also associated with the goddess Isis and was used in temple offerings.
In medieval Europe, peridot was considered a stone of compassion and was believed to have healing properties. It was thought to help with asthma, sinus issues, and digestive problems. Some legends held that peridot could drive away nightmares and protect against enchantments. In modern crystal healing practices, peridot is often associated with the heart chakra and is believed to promote emotional balance, reduce stress, and attract prosperity and good fortune. It is also considered a stone of growth and renewal, symbolizing the vitality of nature. These metaphysical beliefs, while not scientifically proven, contribute to the gem's enduring popularity and cultural resonance.
Care and Cleaning
Given its moderate hardness and lack of cleavage, peridot is relatively easy to care for, but it does require attention to maintain its luster. As it is not as hard as sapphire or ruby, it can be scratched by harder materials. Therefore, it is advisable to store peridot jewelry separately from other pieces, preferably in a soft cloth or lined jewelry box.
For cleaning, warm soapy water and a soft brush are sufficient. Avoid using ultrasonic cleaners, as the vibrations can potentially damage the stone, especially if it has inclusions. Steam cleaning is also not recommended due to the risk of thermal shock. Peridot should be kept away from harsh chemicals, including household cleaners, chlorine, and strong acids, which can etch the surface. When worn regularly, it is best to put peridot jewelry on after applying cosmetics and perfumes to minimize exposure to chemicals. With proper care, peridot jewelry can retain its vibrant color and shine for generations.
Conclusion
Peridot stands out as a gemstone with a remarkable story, from its deep-earth and extraterrestrial origins to its long history in human adornment. As the birthstone for August, it carries the legacy of ancient Egyptian sun worship, medieval clergy, and modern gem enthusiasts. Its unique olive-green color, derived from iron in the Earth's mantle, and its durability make it a beloved choice for jewelry. While its metaphysical beliefs add a layer of cultural significance, its true value lies in its natural beauty and fascinating geological history. Whether set in an ancient amulet or a contemporary ring, peridot continues to captivate with its vibrant hue and enduring appeal.