Turquoise is a captivating bluish-green phosphate mineral, rich in copper and aluminium, that has been prized for millennia. Renowned for its distinctive color and historical allure, it serves as a significant gemstone for collectors, jewelry enthusiasts, and those who follow birthstone traditions. Because of its scarcity in high grades and the specific geological conditions required for its formation, turquoise remains a highly sought-after mineral in the global market.
History and Lore
The historical journey of turquoise is deeply intertwined with global trade and cultural perception. The gemstone's very name provides a clue to its early movement into Europe; the term is derived from "Turkey," as the first turquoise gemstones reached Europe via that country, with "turquoise" meaning "Turkish" in ancient French.
Throughout history, turquoise has been valued not only for its aesthetic beauty but also for its perceived spiritual and medicinal properties. In various cultural traditions, the stone has been associated with healing. Modern new age gem healers continue this legacy, placing deep faith in the stone's ability to provide relief from specific ailments, including diabetes, tuberculosis, and jaundice.
Geological Formation and Sources
Turquoise deposits are not common globally, as they require very specific geological conditions to form. This scarcity contributes to the high value of genuine, high-grade specimens. The gemstone is sourced from several key regions across the world, each offering distinct characteristics:
Iranian (Persian) Sources
Iran, specifically the mines near the city of Nishapur, has produced turquoise for thousands of years. Persian turquoise is widely regarded as some of the most valuable in the world due to its intense, well-balanced blue color and superior durability. The Nishapur mines are particularly noted for producing the hardest natural turquoise.
American Sources
The United States is a prolific source of turquoise, with several renowned mines: - Arizona: Mines such as Kingman and others in Arizona produce exceptional quality stones. - Nevada: Lander County is home to the "Lander Blue" turquoise, a scarce variety prized for its "spiderweb" pattern. Due to limited mine capacity, only about one hundred pounds of this specific stone were ever extracted. - Other Notable Sources: "Bisbee" and "Sleeping Beauty" are also recognized as sources of good quality American turquoise, although a majority of these stones are stabilized.
Other Sources
Tibetan turquoise is another recognized variety, though it often features a matrix pattern. In certain contexts, such as astrological evaluations, this matrix pattern can lead to a reduction in the stone's perceived value compared to clear, blue specimens.
Gemological Properties
Turquoise is characterized by its unique chemical composition and physical properties, which influence both its beauty and its durability.
Chemical Composition and Color
As a copper and aluminium-rich phosphate mineral, turquoise naturally exhibits a range of colors from cloudy blue to green. The most prized color is the "Persian blue," often referred to in the trade as "sky blue" or "robin egg blue," characterized by a consistent and intense hue. Genuine turquoise often features black or brown veins, whereas fake versions frequently appear as a pure, vibrant blue that lacks the natural depth of the real mineral.
Hardness and Durability
In its natural state, turquoise is considered highly fragile. It reaches a maximum hardness of 6 on the Mohs scale, making it slightly harder than ordinary glass. Because of this inherent fragility, many turquoise stones are "stabilized" or treated before they are set into jewelry to increase their durability. The most durable natural specimens are typically those found in the Nishapur mines of Iran.
Determining Value and Pricing
The market for turquoise is complex, with prices ranging from as low as $0.01 per carat for synthetic versions to $1,000 per carat for superior, rare specimens.
The Turquoise Quality Index (TQI)
To standardize the valuation of these stones, the Turquoise Quality Index (TQI) is utilized. The TQI is a scoring system on a scale from 8 to 100, where a higher number indicates a higher grade and greater value. The TQI is determined by evaluating eight indicators based on the stone's physical structure and rarity. However, because factors like color, clarity, and pattern can be subjective, TQI scores may vary slightly depending on the evaluator.
The relationship between weight and quality is expressed through the following formula: Turquoise Price = Weight (Carat) × Turquoise Quality Price/Carat Index (TQI)
Market Grade Breakdown
The following table provides a detailed breakdown of the TQI scoring system and the corresponding market values:
| TQI Score | Grade | Market Grade % | Price per Carat |
|---|---|---|---|
| 90-100 | AAAA | Superior (less than 1%) | $50 - $1,000 |
| 85-89 | AAA | High (2%) | $10 - $50 |
| 75-84 | AA | 5% | $2.50 - $10 |
| 65-74 | A | Medium (10%) | $1.00 - $2.50 |
| 35-64 | B | Low (22%) | $0.05 - $1.00 |
| 17-34 | Reconstituted | Fabricated (60%) | $0.02 - $0.05 |
| 8-16 | Synthetic | N/A | $0.01 |
Factors Influencing Price
Several key factors determine whether a stone will sit at the bottom or the top of the price spectrum: - Origin: Iranian turquoise typically commands the highest prices due to its rarity and intense color. Rare American stones, such as genuine Lander Blue, can reach $400 to $600 per carat. - Color: Consistent, intense blue hues (Persian blue) are the most valuable. - Rarity: Limited-production mines increase the value. For example, one pound of pure, hard Persian blue turquoise can potentially cost more than two million dollars. - Authenticity: The market is flooded with fakes; approximately 90% of turquoise available daily is considered fake or synthetic. Genuine pieces, therefore, command a significant premium. - Weight: Turquoise is measured in carats (5 carats = 1 gram). Generally, heavier stones are more valuable.
Identification and Market Risks
For the jewelry buyer or collector, distinguishing between natural and treated or synthetic turquoise is critical.
Genuine vs. Fake
Natural turquoise is typically cloudy blue or green and often contains black or brown veins. In contrast, synthetic or fake stones often appear as a "pure" blue and lack the natural vibrancy and characteristics of genuine minerals. Much of the jewelry marketed as turquoise is actually made from highly treated or synthetic materials.
Stabilization
Due to its low Mohs hardness, many genuine stones undergo stabilization. This process fills the porous structure of the stone with resin to make it more durable for wear. While common in American turquoise (such as Kingman or Sleeping Beauty), the distinction between "natural" (unstabilized) and "stabilized" stones can affect the collector's value.
Practical Examples of Market Value
To illustrate the wide variance in turquoise pricing, consider the following examples of high-value specimens: - A 402-gram unstabilized Kingman Turquoise from Arizona was offered at $2,750. - A 1,218-gram natural deep-blue spiderweb Persian turquoise pyrite rough was valued at $1,250. - A unique 5.9-inch carved turquoise crystal skull reached a value of $25,000.
Conclusion
Turquoise remains a gemstone of profound significance, blending geological rarity with thousands of years of cultural and medicinal lore. From the high-grade, durable blue stones of Nishapur to the rare spiderweb patterns of Lander Blue, the variety within this mineral is vast. While the market is heavily saturated with synthetic alternatives, genuine high-grade turquoise—characterized by its specific TQI score, origin, and natural color—continues to be a prized asset for collectors and jewelry enthusiasts alike. Its journey from the mines of Iran and the American West to the global jewelry market underscores its enduring appeal as both a luxury item and a symbol of status.