Peridot, the vibrant green gemstone, is the gem-quality variety of the mineral olivine, one of the most abundant minerals on Earth. Unlike most gemstones that form within the Earth’s crust, peridot crystallizes deep within the planet’s mantle. This extraordinary origin, spanning from deep terrestrial rock to fragments of space debris, makes it a geologically fascinating gem. The varied locations where peridot is found reflect the forces and cosmic events that brought this gem to the surface.
The Deep-Earth Origin of Peridot
The formation of gem-quality peridot begins in the upper mantle, a layer extending roughly 40 to 400 kilometers below the surface. This region is primarily composed of peridotite rock, which is rich in olivine. The mineral is stable under the immense pressures and high temperatures found at these depths, existing in large, coarse-grained masses.
The process that brings these crystals to the surface is linked to specific types of volcanic activity. Peridot crystals are often found encased in basalt, a dark, fine-grained volcanic rock formed from rapidly cooling lava. As magma rises from the mantle, it sometimes tears away solid fragments of the surrounding rock.
These fragments, known as xenoliths, are pieces of the mantle carried to the surface within the magma flow. The peridot crystals remain intact within these xenoliths or as nodules in the basalt. They are protected from melting by the magma’s rapid ascent, which explains why peridot is associated with volcanic regions across the globe.
Primary Global Sources for Commercial Mining
The majority of the world’s commercial peridot supply comes from a limited number of prolific sources, most notably the United States. The San Carlos Apache Indian Reservation in Arizona is the world’s largest producer, supplying an estimated 80 to 95 percent of the global market. Peridot here is recovered from the basalt flows on Peridot Mesa, where the crystals are found as small, irregular nodules in the volcanic rock.
The mining process in Arizona focuses on collecting these nodules from the weathered basaltic rock covering the mesa. Although the crystals are typically smaller than those from other locations, their abundance makes the San Carlos Reservation the dominant force in commercial production. The stones are known for a characteristic bright, yellowish-green hue.
A second major source for high-quality, larger stones is the border region of Pakistan and Afghanistan, particularly the Supat and Sapat Gali areas. These deposits, located high in the Himalayan mountains, were discovered in the 1990s and became known for their exceptional clarity and size. The geological setting in this region differs from the volcanic nodules of Arizona, with crystals often found in veins within metamorphosed mantle rock. These Pakistani peridots frequently display a richer, deeper green color and can yield cut stones exceeding 100 carats, establishing their place in the fine jewelry market.
Secondary and Historically Significant Deposits
Before modern discoveries, the island of Zabargad (St. John’s Island) in the Red Sea was the world’s main source of peridot for centuries. Located off the coast of Egypt, this island was mined as early as the 3rd century BC and supplied the ancient world with the gem. The peridot deposits here are linked to the uplift of mantle rocks along the spreading zone of the Red Sea rift.
While Zabargad is no longer a significant commercial producer, other international sources contribute to the market, often yielding stones with unique characteristics. Myanmar, particularly the Mogok Valley, is a renowned historical source for some of the finest peridot. It is celebrated for its deep, intense green color and high clarity, and these stones are often recovered from alluvial deposits.
More recently, China and Vietnam have emerged as important secondary producers, with deposits often found in volcanic regions similar to Arizona. Chinese peridot, sourced from areas like the Tibetan Plateau, tends to be lighter in color but is an abundant commercial source. Other minor deposits are scattered across locations like Australia, Norway, and Brazil.
Extraterrestrial Discovery: Peridot in Meteorites
Peridot is one of the few gemstones known to have an extraterrestrial origin, found in a rare type of stony-iron meteorite called a pallasite. These meteorites are believed to have formed at the boundary between the metallic core and the rocky mantle of a shattered asteroid. The peridot crystals, which are silicate components, became suspended within a matrix of iron-nickel metal as the asteroid cooled.
These cosmic fragments fall to Earth, providing scientists with samples of material from the early solar system, estimated to be over four billion years old. The peridot found in pallasites is extremely rare in gem quality, and faceted stones are typically very small, often less than one carat. Their unique composition and origin make them a highly prized material for collectors.