Peridot is a green gemstone known for its distinctive lime to olive color. It is one of the few gemstones whose color is derived from an internal component of its chemical structure, rather than from trace impurities. This unique characteristic means the stone appears only in green, though the hue and intensity can vary significantly. The gem’s striking color and transparency have made it a popular choice for jewelry throughout history.
Geological Identity of Peridot
Peridot is the gem-quality variety of the common mineral olivine, a magnesium iron silicate. Its chemical formula is (Mg,Fe)₂SiO₄, where the iron content is directly responsible for the signature green coloration. Unlike most gemstones that crystallize within the Earth’s crust, peridot is one of only two gems, alongside diamond, that forms deep within the planet’s mantle.
This process requires intense heat and pressure, occurring at depths between 20 and 55 miles below the surface. Peridot crystals are brought to the surface through violent geological events, such as volcanic eruptions, embedded within volcanic rocks like basalt. These crystals are often found as irregular, rounded rocks known as nodules within lava flows.
The stone’s origins are not limited to Earth, as peridot crystals have also been identified in pallasite meteorites. These extraterrestrial samples originated in the asteroid belt, offering a glimpse into the early materials of our solar system. The presence of olivine in meteorites confirms that this mineral is a common component of cosmic matter.
Physical Characteristics and Appearance
The characteristic green color of peridot is inherent to its composition, a trait known as idiochromatic. The specific amount of iron substituting for magnesium within the crystal lattice determines the resulting shade. A higher iron content produces a deeper, olive-green hue, while stones with less iron tend toward a brighter, yellowish-green or lime color.
Peridot is rated between 6.5 and 7 on the Mohs scale of hardness, placing it in the moderately durable range for jewelry use. This hardness rating means the stone is resilient enough for most settings but is susceptible to scratching when it contacts harder gems like sapphire or diamond. The material also possesses fair to good toughness, which means it can be vulnerable to fracturing from hard impacts or sudden temperature changes.
Most high-quality peridot is transparent. Common internal features, known as inclusions, are sometimes present and can take the form of small, reflective mineral discs colloquially described as “lily-pads.” These internal characteristics are used by gemologists to identify and authenticate the natural origin of the stone.
Origins and Cultural Significance
The history of peridot mining can be traced back more than 3,500 years to Zabargad Island, now known as St. John’s Island, in the Red Sea off the coast of Egypt. The ancient Egyptians were the first to systematically mine the gem, referring to it as the “Gem of the Sun” due to its fiery glow. It was believed to possess protective powers against the terrors of the night and evil spirits.
For centuries, this island remained the world’s primary source for the stone. Peridot from this region was often historically misidentified as emerald. The name “peridot” itself is thought to be derived from the Arabic word faridat, meaning “gem.”
Today, the majority of the world’s commercial supply comes from the San Carlos Apache Indian Reservation in Arizona. Other major modern sources include the Mogok region of Myanmar, known for producing fine-colored crystals, and the mountainous areas of Pakistan. Peridot is also recognized as the traditional birthstone for the month of August.
Care and Maintenance of Peridot Jewelry
Given its moderate hardness, peridot jewelry requires careful maintenance to ensure its longevity. The best method for cleaning is using warm, mildly soapy water and a soft-bristled brush to gently remove dirt and oils. Rinse the piece thoroughly with clean water afterward to remove all soap residue.
The stone’s chemical structure makes it vulnerable to attack by various acids, including the mild acidity in human perspiration. Because of this susceptibility and its sensitivity to thermal shock, both ultrasonic and steam cleaners should be avoided completely, as they can cause irreparable damage or fracture the gem.
When storing peridot pieces, keep them separate from harder gemstones such as diamonds, rubies, and sapphires. Storing the jewelry in a soft pouch or a fabric-lined compartment prevents accidental scratching. Protecting the stone from sudden or extreme temperature changes will help maintain its structural integrity and brilliance.