Introduction

Turquoise, a hydrated copper aluminium phosphate mineral with the chemical formula CuAl₆(PO₄)₄(OH)₈·4H₂O, stands as one of humanity’s most cherished gemstones. This secondary mineral is deposited from circulating waters and occurs chiefly in arid environments as blue to greenish, waxy veinlets in alumina-rich, weathered, volcanic rocks. With a specific gravity ranging from 2.6 to 2.8 and a refractive index between 1.61 to 1.65, turquoise displays a characteristic waxy lustre and is typically opaque to light.

The mineral’s captivating appeal stems from its remarkable colour range and relative ease of working. Turquoise appears in shades of sky blue, blue-green, green, greenish-yellow, and greyish-green. The prized sky-blue colour indicates high quality, while greenish-yellow tones suggest lower-grade material. The blue colouration results from copper ions in the mineral’s structure, while iron substitution for aluminium creates greenish hues.

Turquoise crystallises in the triclinic system but most commonly occurs in an amorphous form as veins and scattered grains within host rocks. Its relatively low hardness and natural porosity make the mineral vulnerable to physical and chemical damage. Consequently, many turquoise specimens undergo treatment with oil, paraffin, or liquid plastics to fill voids, increase hardness, and prevent colour changes.

Natural turquoise colour may gradually fade over time, reducing its value. Prolonged exposure to intense light or heat causes colour degradation and depreciation. At 250°C, blue turquoise transforms to a dull green colour. Colour changes in turquoise gemstones can result from sunlight exposure, evaporation of natural water content, or contact with chemicals in cosmetics. Therefore, it’s advisable to remove turquoise rings when washing hands, as the mineral easily accumulates dirt and contaminants, and even breathing moisture can have adverse effects.

Types and Classification of Turquoise

Traditional Persian classification of turquoise is based on name, type, and colour characteristics:

Ajami Turquoise: Round and large specimens of nearly pure turquoise in deep blue colour, representing the most expensive variety.

Shajari Turquoise: Contains waste rock that, after cutting, reveals branching or dendritic patterns.

Chaghale Half-Colour: Similar to Ajami but with less intense colour and white spots (alunite mineral inclusions).

Chaghale White: Similar to half-colour but much lighter in appearance.

Shokofe Turquoise: Smaller than Chaghale varieties with minimal turquoise content.

Arabic Turquoise: Features flat cuts with a shorter diameter than Shajari types, displaying pale green colouration. Larger diameter specimens are called “Dobehri turquoise.”

Tofal Colourful: Similar to Shajari with less waste rock.

Tofal Half-Colour: Same as colourful Tofal but with lighter colouration.

Tofal White: Very light-coloured version, sometimes called “Shirbo.”

Chal or Soft Turquoise: Very fine turquoise (slightly larger than lentils) used for decorating objects.

Coarse Turquoise: Large stones containing thin, scattered turquoise veins, representing the lowest grade from Neyshabur.

Khake Turquoise: Spherical forms of various sizes without waste rock, found within altered and fractured veins.

Gol Kasni Turquoise: Green-coloured turquoise (greyish-green), also called “bitter turquoise” due to Fe³⁺ cations in its structure.

Chemical Turquoise: Artificial turquoise created by colouring chalcedony or mixing glass, plastic, and blue dyes.

Historical Significance

Archaeological discoveries from the Deh Luran Plain in western Iran indicate that turquoise was first utilised around 7000 BCE. The oldest worked turquoise stone discovered globally was found 5.8 meters underground, 22 kilometres from Neyshabur, on the belt of a 7,000-year-old human skeleton.

Since the second millennium BCE, turquoise has been used as an ornamental stone in Iran. Foundation inscriptions from Darius the Great’s palace in Susa reveal that turquoise was called “Akhshayin” and imported from Khwarezm for palace decorations. During the Sassanid period, beyond rings and earrings, turquoise vessels were crafted for royal courts, referred to as “Parang,” “Paruzak,” or “Piruzak.”

The name “turquoise” derives from the French word meaning “Turkish,” as these stones first reached Europe via Turkey, though their origins are Iranian. In Iran, turquoise is known as “Firoozeh,” meaning victory in Persian.

The Legend of Shaddad and Turquoise Discovery

Persian tradition preserves a fascinating legend about the discovery of Neyshabur’s turquoise mines. According to this tale, when Shaddad reached the peak of his power, he proclaimed himself divine and decided to create an earthly paradise. He sent messengers worldwide to gather all beautiful things for this magnificent construction. They discovered turquoise in Neyshabur’s mountains and used it to adorn the branches of paradise trees.

Another version states that when Shaddad’s legendary paradise was completed and its streams began flowing, his people scoured the earth for the most precious and enchanting stones to decorate these waterways. Upon reaching Neyshabur, they found turquoise, which became the legendary sand of Shaddad’s paradise. A cave named “Shaddad’s Cave” allegedly exists in this mine, supporting the legend.

This legend, whether factual or not, highlights two important points: it demonstrates the ancient history of Neyshabur turquoise mining, as folklore typically develops around phenomena of unclear origin and mysterious appearance. Additionally, since this mine has long been the focus of human greed and competition, attributing its discovery to Shaddad (a symbol of worldly desire and avarice) provides satirical commentary on human ambition.

Formation and Geology of Iranian Turquoise

Among Iran’s turquoise mines, Neyshabur turquoise mine is one of the most important in the country and even at the world level, with its excellent quality, especially the Ajami and Shajri varieties giving it a special reputation. Iranian turquoise deposits are reported from various regions, including Neyshabur, Damghan, Shahrbabak, Tabas, Kashmar, and Anarak, but Neyshabur has the highest quality and most expensive turquoise in the world, with mines capable of producing up to 50 metric tons annually.

Research indicates that turquoise formation begins with the surface oxidation of sulphide minerals like chalcopyrite, which, combined with sulfuric acid and geochemical effects on clay minerals, leads to turquoise formation. In this process, copper, necessary for turquoise formation, is supplied through groundwater flow from greater depths.

In Neyshabur’s turquoise mine, field and laboratory studies reveal volcanic rocks (trachyte, hornblende trachyte, andesite, latite) and semi-deep rocks with diorite porphyry composition. These units have undergone silicic, argillaceous, carbonate, and weak propylitic alterations. Mineralisation occurs in both volcanic and intrusive rocks, involving primary and secondary stages.

Primary mineralisation appears as disseminated and hydrothermal forms, with hydrothermal breccias being particularly important. Two mineralisation phases exist: pre-brecciation and post-brecciation, with the latter formed by silicic solutions. Secondary mineralisation includes turquoise, chalcocite, covellite, hematite, and goethite.

Enhancement and Treatment

A significant portion of gemstones from natural sources requires enhancement due to deficiencies such as poor or pale colour. These shortcomings can be addressed by specialists, and gems can be intensified or lightened as desired. Colouring stones and precious minerals not only increases their value but also enhances market abundance and prosperity.

For colouring turquoise stones, low-grade agate has been used. Since turquoise has a porous structure, coloured salts penetrate the pores and holes, causing colouration. However, most coloured salts don’t integrate into the stone’s original composition, making them unstable and susceptible to decomposition over time.

Copper salts and aniline can be used for colour enhancement. Turquoise imitations often consist of coloured chalcedony or mullite. Crushed or powdered turquoise can be shaped using special adhesives in presses, with glass, ceramics, and plastics used in restoration.

Recently, new types called “stabilised” or “composite” turquoise have appeared in markets, featuring purple, magenta-pink, yellow, green, and blue veining, with some lacking veining entirely. Tests show these specimens consist of rubber and composite materials with turquoise fragments bonded together. The coloured veins are coloured polymers, while vein-free blue samples contain colourless polymers.

A notable development occurred in 1984 when “Zachery turquoise” entered the market, undetectable by conventional methods. This process, developed by E. Zachery, remains proprietary. Research indicates this treatment improves the stone’s polishing ability and colour while reducing porosity and preventing absorption of colour-changing substances like skin oils. These enhanced stones possess geological characteristics similar to natural turquoise without using polymers, identifiable only through chemical analysis (XRF-EDS spectroscopy) due to higher potassium content compared to natural specimens.

Value Assessment and Care

Colour represents the primary factor determining turquoise value. Sky-blue turquoise possesses the highest quality, while increasing white or green colouration reduces value. Additionally, turquoise should not be chalky or soft, as such material lacks sufficient durability and loses colour more rapidly, making it unsuitable for jewellery use.

Most turquoise contains black or brown veining from iron oxides or host rock filling cracks and fractures. These veins form regular or irregular patterns called “spider web matrix,” known in Iranian markets as “Shajari turquoise.” Beautiful, regular patterns enhance turquoise value, while irregular, spotty networks diminish it.

Craftsmanship quality, polish standard, and symmetry significantly impact turquoise value. Special attention is required when identifying turquoise, as some specimens are coloured before waxing, while others undergo reconstruction by powdering small, unusable pieces, melting them, and creating new pieces in standard cabochon and bead designs using special molds.

Heat and direct sunlight exposure reduce turquoise quality. At 250°C, blue turquoise transforms to dull green. Cosmetics, chemicals, and oils also adversely affect turquoise quality. The optimal storage method involves placement in moist sawdust or sand.

Proper Care and Maintenance

With lower hardness comes greater porosity, making turquoise vulnerable to damage and colour changes from chemical exposure. This mineral contains aluminium phosphate copper, and appears in blue, blue-green, and green colours. Today, it remains a popular semi-precious stone used with silver and gold. Colour variation in turquoise results from copper content and quantity in the composition.

Care Recommendations:

Cleaning: Use a soft, damp cloth for cleaning. Cover the surface with cloth and gently rub to completely remove spots and excess materials. Heat or solvents can damage treated surfaces.

Drying: Allow specimens to air dry completely in open air before returning to storage.

Activity Precautions: Remove turquoise jewellery during dishwashing, diving, swimming, and when using perfumes or sprays, reapplying after activity completion.

Storage: Store turquoise separately in closed containers away from other jewellery due to its low hardness and susceptibility to damage from contact with other minerals.

Work Limitations: Avoid wearing turquoise rings during heavy work such as house cleaning, car repair, gardening, painting, and similar activities.

Cleaning Methods: Avoid ultrasonic cleaning for turquoise jewellery. Ultrasonic cleaners use chemicals that can damage the turquoise appearance. If stones are set in sterling silver, prevent any silver cleaner drops from contacting the stone.

Investment Value: Purchasing turquoise can be a good investment for future sale. However, due to its rarity, many counterfeit versions exist, requiring purchases from reputable sources with expert consultation.

Common Damage Factors:

The two most common destructive factors for turquoise are physical scratches or severe impacts due to its relative softness, and exposure to oils, soaps, lotions, and similar substances. Since natural turquoise is somewhat porous, chemicals and oils can penetrate and cause colour changes.

The best prevention method is avoiding turquoise use during heavy work. Once the colour change begins, unfortunately, the colour alteration is complete and irreversible. Even with daily care during use of natural turquoise, if the stone initially tends toward green, you may not notice gradual colour changes under normal conditions.

Final Care Instructions:

• Always remove turquoise rings and bracelets before dishwashing, gardening, wall painting, car repairs, and other dirty household tasks, as household bleach can permanently affect turquoise colour.
• Hand lotion can alter stone colour, so apply perfume, lotion, etc., first, then wear turquoise jewellery.
• Never use ultrasonic devices for turquoise cleaning.
• Avoid wearing turquoise rings in swimming pools, as chlorine significantly causes turquoise colour changes.
• Bathing with turquoise is prohibited, as soap negatively affects the turquoise colour.
• Avoid using chemicals with turquoise jewellery or exercise extreme caution to prevent contact, as acids in some chemicals can alter the stone colour.

Global Significance

Turquoise is the national gemstone of Iran, and the Neyshabur deposit is known for yielding turquoise with unique colour and quality, historically known as “Persian turquoise”. Other turquoise-producing countries include Egypt, the United States, China, Australia, Germany, Ireland, Chile, Brazil, Mexico, Russia, Siberia, Tanzania, Israel, Kazakhstan, Afghanistan, Turkey, and Africa.

Turquoise may be confused with minerals like malachite, chrysocolla, variscite, amazonite, adonatolite, and brochantite. Persian turquoise mines have a similar age to the world’s oldest gem mines, developed before Ancient Egypt around 6000 BC, demonstrating the enduring significance of this remarkable mineral throughout human civilisation.

The legacy of Persian turquoise continues today, with Iranian turquoise being well-known worldwide and used to measure the quality of other turquoise, serving as a scale for comparison. This ancient treasure from the mountains of Neyshabur remains one of nature’s most captivating and culturally significant gemstones.