July and August are months rich in gemological tradition, each associated with multiple birthstones that reflect their unique histories, cultural significances, and physical properties. July's birthstone is the ruby, a gemstone renowned for its deep red hue and symbolic association with love, power, and vitality. August, on the other hand, boasts three birthstones—peridot, sardonyx, and spinel—each with its own distinct character and lore.
The ruby, as the traditional and modern birthstone for July, has been revered for centuries across various cultures for its brilliance and symbolic meaning. August's birthstones, particularly peridot, have long been admired for their greenish glow and their role in ancient beliefs about protection and dreams. Sardonyx, the original August birthstone, and the more recently recognized spinel, complete the month’s gemstone roster with their own compelling histories and properties.
This article explores the historical, cultural, and scientific significance of these gemstones. It delves into their geological origins, symbolic meanings, and modern relevance in jewelry and gemstone appreciation.
History and Lore
The ruby has long been considered one of the most valuable gemstones in the world. Its association with power and vitality can be traced back to ancient civilizations, where it was believed to possess protective qualities. In India, ruby was called the “king of precious stones,” symbolizing power and youthful energy. In medieval Europe, rubies were thought to bestow health, wisdom, wealth, and success in love. Burmese warriors even believed that wearing a ruby made them invincible in battle.
Peridot, the primary modern birthstone for August, has a rich history rooted in myth and superstition. Ancient cultures used peridot as a protective talisman, believing it could ward off nightmares and evil spirits. The ancient Hawaiians thought that peridot was the tears of the goddess Pele, brought to the surface by volcanic eruptions. In medieval Europe, peridot was often mistaken for emerald and topaz due to its greenish hue, and it was even used to decorate the Shrine of the Three Holy Kings in Germany’s Cologne Cathedral.
Sardonyx, the original August birthstone, has been known and used for over 4,000 years. It was a popular gemstone in ancient Egypt, Greece, and Rome, often carved into intricate cameos and seals. Sardonyx was believed to bring courage and strength, and it was also used as a protective stone in ancient times.
Spinel, the newer addition to the August birthstone list, was long mistaken for ruby and other red gemstones. Its recognition as a distinct gemstone has gained popularity in recent years, and it is now appreciated for its vibrant colors and durability. Spinel is also the gemstone for the 22nd wedding anniversary, symbolizing immortality and enduring love.
Geological Formation and Sources
Ruby
Rubies are a variety of the mineral corundum, which is composed of aluminum oxide (Al₂O₃). The intense red color of ruby is due to the presence of trace amounts of chromium. The finest rubies display a deep red with a hint of purple, known in the trade as “pigeon’s blood.” This color is highly sought after and commands premium prices in the gemstone market.
Rubies are formed under high-pressure and high-temperature conditions deep within the Earth’s crust. They are found in metamorphic rocks and are often associated with marble and pegmatite formations. The most famous sources of rubies include Burma (Myanmar), Sri Lanka, Thailand, and Tanzania. Burmese rubies are particularly prized for their vivid color and exceptional quality.
Peridot
Peridot is the yellowish green to greenish yellow gem variety of the mineral olivine. Its color is due to the presence of iron in its chemical composition. Peridot is unique among gemstones in that it can also be found in meteorites and on the Moon and Mars. This extraterrestrial origin adds to the mystique of peridot and makes it one of the few gemstones with a cosmic connection.
Peridot is formed in the Earth’s mantle and is brought to the surface through volcanic activity. It is also found in lava flows and in the dust of meteorites. The finest peridots are typically sourced from Egypt, Myanmar, and the United States. Historically, the Egyptian island of Zabargad (formerly known as Topazios) was the primary source of peridot, and it has been mined since around 340–279 BCE.
Sardonyx
Sardonyx is a type of chalcedony, a microcrystalline quartz. It is characterized by its reddish-brown and white banding, which makes it ideal for carving into cameos and intaglios. The banding in sardonyx is caused by the alternating layers of silica-rich and iron-rich material during its formation.
Sardonyx is typically formed in sedimentary rocks and is often found in association with other chalcedony varieties. The finest sardonyx is known for its clear and distinct layering, with sharp contrasts between the red and white bands. Sardonyx has been mined for thousands of years in regions such as India, Greece, and Egypt. It is also found in modern times in countries like Brazil, Uruguay, and the United States.
Spinel
Spinel is a mineral composed of magnesium aluminum silicate (MgAl₂O₄). It can occur in a wide range of colors, including red, pink, orange, purple, blue, black, and even colorless. The red spinel, often mistaken for ruby in the past, has gained recognition as a distinct and valuable gemstone.
Spinel is formed in both igneous and metamorphic rocks and is found in various parts of the world, including Burma, Sri Lanka, Afghanistan, and Tanzania. The gemstone is known for its durability, with a hardness of 8 on the Mohs scale. This makes it suitable for use in everyday jewelry, as it can withstand wear and tear.
Gemological Properties
Ruby
- Mineral: Corundum
- Chemical Composition: Aluminum oxide (Al₂O₃) with trace chromium
- Color: Deep red with a hint of purple (pigeon’s blood)
- Hardness (Mohs Scale): 9
- Refractive Index: 1.76–1.78
- Specific Gravity: 4.00
- Transparency: Transparent to translucent
- Luster: Vitreous
Rubies are among the hardest natural gemstones, second only to diamonds. Their deep red color is due to the presence of chromium. The most valuable rubies are those with a “pigeon’s blood” color, which is a deep red with a slight purple undertone. Rubies are also known for their brilliance and fire, making them highly desirable in fine jewelry.
Peridot
- Mineral: Olivine
- Chemical Composition: Magnesium iron silicate (Mg,Fe)₂SiO₄
- Color: Yellowish green to greenish yellow
- Hardness (Mohs Scale): 6.5–7
- Refractive Index: 1.65–1.69
- Specific Gravity: 3.34
- Transparency: Transparent
- Luster: Vitreous
Peridot is known for its vibrant green color, which is caused by the presence of iron. It has a hardness of 6.5 to 7 on the Mohs scale, making it relatively durable but not as hard as ruby. Peridot is a uniaxial gemstone, meaning it has one optic axis, and it is also birefringent, which means it can split light into two rays.
Sardonyx
- Mineral: Chalcedony
- Chemical Composition: Silica (SiO₂) with iron oxide
- Color: Red and white banding
- Hardness (Mohs Scale): 6.5–7
- Refractive Index: 1.53–1.54
- Specific Gravity: 2.58–2.61
- Transparency: Translucent to opaque
- Luster: Waxy to vitreous
Sardonyx is a type of chalcedony, which is a microcrystalline form of quartz. It is known for its distinct red and white banding, which is caused by the alternating layers of silica-rich and iron-rich material. Sardonyx has a hardness of 6.5 to 7 on the Mohs scale, making it suitable for use in carved cameos and seals.
Spinel
- Mineral: Spinel
- Chemical Composition: Magnesium aluminum silicate (MgAl₂O₄)
- Color: Red, pink, orange, purple, blue, black
- Hardness (Mohs Scale): 8
- Refractive Index: 1.718
- Specific Gravity: 3.60
- Transparency: Transparent to translucent
- Luster: Vitreous