Peridot, a gem celebrated for its vibrant green hues, holds a unique position in the world of gemstones. Formed not only within the Earth’s crust but also in the molten rock of the upper mantle and even discovered within meteorites, peridot boasts a fascinating origin story. This article delves into the history, geological formation, gemological properties, and cultural significance of this captivating August birthstone, drawing exclusively from available sources.
History and Lore
Peridot has been valued since ancient times, with a history steeped in superstition and reverence. Throughout civilizations, it was believed to possess protective powers, capable of warding off fears and nightmares. This belief stemmed from a perceived “inner radiance” the stone imparted, sharpening the mind and fostering awareness, ultimately aiding in the recognition of one’s destiny and spiritual purpose.
Historical accounts reveal a tendency to confuse peridot with other green gemstones, notably emerald beryl. This misidentification is noted in descriptions of treasures within historical artifacts, such as those found in the Dom of Cologne, Germany. The gemologist G.F. Kunz specifically addressed this confusion in his studies of church treasures.
Geological Formation and Sources
Peridot’s formation is remarkable, occurring in both mafic and ultramafic rocks, including lava and peridotite xenoliths originating from the Earth’s mantle. Unlike many gemstones formed within the Earth’s crust, peridot is one of only two gems – the other being diamond – known to originate in the molten rock of the upper mantle. This deep-earth origin contributes to its relative rarity on the surface, as it is susceptible to alteration during its journey upwards and weathering once exposed.
Currently, the primary source of peridot is the San Carlos Apache Indian Reservation in Arizona, accounting for approximately ninety percent of the world’s supply. Additional mining locations exist within the United States, including Arkansas, Hawaii, Nevada, and New Mexico’s Kilbourne Hole. Internationally, peridot is also sourced from Australia, Brazil, China, Egypt, Kenya, Mexico, Myanmar (Burma), Norway, Pakistan, Saudi Arabia, South Africa, Sri Lanka, and Tanzania.
Remarkably, peridot crystals have also been collected from pallasite meteorites, offering a cosmic connection to the gem. Pallasitic peridot differs chemically from its terrestrial counterpart, notably lacking nickel. Notable meteorites containing peridot include those from Indonesia (Jeppara), Brenham, Esquel, Fukang, and Imilac.
Gemological Properties
Peridot belongs to the silicate mineral category, with a chemical formula of (Mg,Fe)2SiO4. It crystallizes in the orthorhombic system. The color range of peridot is typically yellow to yellow-green, olive-green, or brownish, though some specimens exhibit a vibrant lime green or even an emerald hue.
Several gemological properties define peridot’s characteristics. It registers between 6.5 and 7 on the Mohs scale of hardness, indicating moderate durability. Its luster ranges from vitreous to oily, and it exhibits a colorless streak. Peridot is generally translucent to transparent, with a specific gravity ranging from 3.2 to 4.3.
Refractive index readings for faceted peridot gems typically fall around α = 1.651, β = 1.668, and γ = 1.689, with a biaxial positive birefringence of 0.036–0.038. Increasing iron concentration within the gem leads to darker coloration, increased specific gravity, and shifts in refractive indices. The iron-rich end-member of the olivine solid solution series is known as fayalite.
Peridot exhibits weak pleochroism, displaying pale yellow-green to yellow, or yellow to yellow-orange hues depending on the viewing angle. It is infusible, meaning it does not melt easily, but thermal shock should be avoided. The gem slowly forms gelatinous silica when exposed to hydrochloric acid.
Inclusions within peridot can include magnesium-rich minerals like pyrope and magnesiochromite, often surrounded by “lily-pad” cleavages. Biotite flakes, appearing flat, brown, translucent, and tabular, are also commonly observed.
Symbolism and Metaphysical Beliefs
Beyond its aesthetic appeal, peridot has long been associated with symbolism and metaphysical properties. Ancient beliefs attributed protective qualities to the stone, shielding wearers from negative energies and promoting restful sleep. The concept of “inner radiance” suggests that peridot enhances mental clarity, fosters self-awareness, and facilitates the realization of one’s life purpose.
Care and Cleaning
Due to its hardness of 6.5-7 on the Mohs scale, peridot requires careful handling to avoid scratches and damage. Cleaning can be performed with warm, soapy water and a soft brush. Avoid harsh chemicals or ultrasonic cleaners, as these may damage the stone. Given its susceptibility to thermal shock, sudden temperature changes should be avoided.
Conclusion
Peridot stands as a remarkable gemstone, distinguished by its unique origins, vibrant color, and rich history. From its formation in the Earth’s mantle and discovery within meteorites to its enduring symbolism and protective qualities, peridot continues to captivate and inspire. As the birthstone for August, it represents a connection to both terrestrial and cosmic realms, offering a glimpse into the wonders of the natural world.