Arizona peridot — also widely known in the trade as San Carlos peridot — is gem-quality olivine mined on the San Carlos Apache Reservation in Graham and Gila counties of south-eastern Arizona, United States. The deposit is, by volume, the single largest source of commercial peridot on earth, supplying the majority of the world's faceted peridot available in the lower and mid-market price ranges. Characterised by a yellowish-green to medium green colour, reliable eye-clean clarity, and a consistent supply of stones well above one carat, Arizona peridot has become the benchmark material against which other peridot origins are commercially measured.

Geological Origin

The San Carlos deposit is a classic example of mantle-derived peridot. The olivine crystallised deep within the upper mantle and was transported to the surface encased in ultramafic xenoliths — fragments of mantle rock — carried by Pliocene and Pleistocene basaltic volcanism. The host basalt flows are exposed across the reservation, and the xenoliths weather out of the matrix to concentrate in alluvial gravels and residual soils. This mode of occurrence is shared with other volcanic peridot localities worldwide, including Zabargad (Egypt) and deposits in China and Vietnam, but the sheer areal extent of the San Carlos flows and the density of olivine-bearing xenoliths make the Arizona occurrence exceptional in productive capacity.

The olivine at San Carlos is compositionally a forsterite-rich member of the forsterite–fayalite solid-solution series, with an iron content sufficient to produce the characteristic yellow-green hue. Refractive indices fall within the standard peridot range (approximately 1.654–1.690), and the birefringence of approximately 0.036 is high enough to produce the characteristic doubling of back facets visible through the table of larger stones — a useful diagnostic feature in the field.

Colour and Appearance

The colour of San Carlos material is most commonly described as yellowish-green or lime green, with a moderate to moderately strong saturation. It rarely achieves the deeper, more purely green tone associated with the finest Pakistani peridot from the Suppat Valley of Kohistan or the historically prized material from Zabargad. The yellow component, a consequence of iron in the crystal structure, is more pronounced in Arizona stones than in high-altitude Pakistani specimens, which tend toward a purer, slightly cooler green. This distinction is well-recognised among gemmologists and is one of the primary bases for origin determination, though definitive separation of origins requires trace-element analysis or inclusion study rather than colour assessment alone.

Clarity is a notable strength of the San Carlos material. Inclusions, when present, are typically small black chromite or spinel crystals — sometimes arranged in disc-like or halo patterns — and lily-pad stress fractures surrounding fluid inclusions. Many stones in the commercial range are eye-clean, which, combined with the material's natural abundance, makes Arizona peridot highly practical for volume jewellery production.

Mining and Production

Mining on the San Carlos Apache Reservation is conducted under tribal authority, and the Apache people have been the primary miners and sellers of the material for generations. The operation is largely artisanal in character: miners work individual plots, hand-sorting gravels and residual soils for xenolith fragments and loose crystals. The reservation's mineral resources are managed by the San Carlos Apache Tribe, and permits are required for commercial extraction. This community-based structure means production figures are not centrally published, but the trade consistently regards San Carlos as responsible for a substantial majority — commonly estimated at well over half — of the world's commercial peridot supply by weight.

Rough is typically sold through dealers in Globe, Arizona, and at gem shows including the Tucson Gem and Mineral Show, where San Carlos material appears in quantity each February. Sizes available to the trade are generous: stones of 5 to 10 carats in the cut are routine, and clean faceted specimens exceeding 20 carats are obtainable, a size range that would command significant premiums in Pakistani or Burmese material.

Comparison with Other Peridot Origins

Origin is a meaningful value factor in the peridot market, though it remains secondary to colour, clarity, and size. The principal origins and their general trade profiles are:

• San Carlos, Arizona (USA): Highest volume; yellowish-green; affordable; excellent clarity in commercial goods; the standard for mass-market jewellery.
• Suppat Valley, Kohistan, Pakistan: Considered the finest origin for deeply saturated, purely green peridot; large crystals known; commands the highest per-carat premiums.
• Zabargad (St John's Island), Egypt: Historically the most celebrated source, mined since antiquity; production now negligible; stones of documented Zabargad origin are collector items.
• Myanmar (Burma): Produces fine, richly coloured material; limited availability in the current market.
• China (Hebei Province): Significant producer of smaller, often yellowish material; competes with Arizona in the commercial segment.

Gemmological laboratories including GIA and Gübelin have published criteria for peridot origin determination. Inclusion assemblages — particularly the character and arrangement of chromite crystals and the morphology of fluid-inclusion discs — combined with trace-element profiles obtained by laser ablation ICP-MS, allow experienced laboratories to distinguish San Carlos material from Pakistani and other origins with reasonable confidence in clear cases, though overlapping chemistry can complicate borderline specimens.

Treatment

Peridot as a species is not routinely treated, and Arizona peridot is no exception. The material is not known to be heated, irradiated, or filled with resins or glasses in standard commercial practice. Its natural colour is stable under normal conditions, though peridot of all origins is susceptible to deterioration from prolonged acid exposure and from thermal shock, owing to its relatively high birefringence and the internal stresses this implies. Jewellers are advised to avoid ultrasonic and steam cleaning for peridot of any provenance.

In the Trade

Arizona peridot occupies a well-defined niche: it is the go-to material for designers and manufacturers who require clean, attractively coloured peridot in volume at accessible price points. Its abundance has kept per-carat prices modest relative to fine Pakistani material, but this accessibility has also made peridot — as a species — far more visible in mainstream jewellery than it might otherwise be. August's birthstone designation (shared with spinel and sardonyx in the modern list) drives consistent consumer demand, and San Carlos material satisfies the bulk of that demand globally.

In the fine jewellery segment, origin disclosure is increasingly expected. A stone described simply as "peridot" in a commercial context is, statistically, almost certainly of Arizona origin. Dealers offering Pakistani or Burmese material at premium prices are expected to provide laboratory documentation of origin, and buyers at auction should treat unsubstantiated origin claims with appropriate scepticism.

The San Carlos Apache Tribe's stewardship of the deposit gives the material a documented provenance and ethical supply chain that is straightforward to communicate — an advantage in a market increasingly attentive to sourcing transparency.

Further Reading

• GIA Gem Encyclopedia: Peridot — gia.edu
• International Gem Society: Peridot — gemsociety.org