Turquoise 101: Formation, Characteristics, and Varieties

Turquoise, a captivating gem with its vibrant blue-green hues, has enchanted civilizations for millennia. From ancient Egyptian royalty to Native American artisans, this gemstone has been cherished for its beauty and spiritual significance.

Now, join us on a journey through the fascinating world of turquoise as we explore its unique properties, uncover the geological processes that lead to its formation, and discover the various colors and varieties that make it one of the most sought-after gems in the world.

 

Composition and Properties

Turquoise minerals. Left: a solid turquoise from Arizona, USA.
Right: "Big Blue", a large turquoise specimen from the copper mine at Cananea, Sonora, Mexico.

Turquoise is an opaque mineral with a unique chemical composition CuAl₆(PO₄)₄(OH)₈·4H₂O, containing copper, aluminum, phosphate ions, and water molecules. This combination gives turquoise its distinctive properties and appearance. With a hardness of 5 to 6 on the Mohs scale, turquoise is softer than quartz but harder than window glass. Its cryptocrystalline structure rarely forms single crystals, contributing to its unique allure.

Turquoise's color is one of its most captivating aspects, ranging from vivid sky blue or robin's-egg blue to shades of bluish-green, green, and yellowish-green. Copper contributes to the blue tones, while iron adds a greenish tint. The presence of impurities like zinc and chromium can also influence the color and quality of turquoise. Blue minerals are relatively rare, making turquoise's color particularly striking.

The gem's waxy to subvitreous luster and opacity create a unique appearance, making it highly sought-after for jewelry and decorative objects. These properties allow turquoise to be polished to a smooth, attractive finish that showcases its vibrant color and luster.

Turquoise of Madan-e Olya of Nishapur.

Formation: A Geological Wonder

Turquoise's formation is a fascinating geological process that sets it apart from other gemstones. Unlike diamonds and aquamarines, which require immense heat and pressure deep within the Earth, turquoise forms through a sedimentary process at the Earth's surface. As a secondary mineral, turquoise is a porous aggregate of many tiny micro-crystals rather than a single solid crystal.

Chemically, turquoise is a hydrated copper and aluminum phosphate as mentioned above, and its growth environment may introduce impurities like iron and zinc. The formation process begins in arid environments, where meteoric water percolates through copper-rich rocks, creating a soluble, acidic solution that interacts with aluminum and potassium minerals. Under specific conditions, turquoise precipitates in cavities and fractures, gradually forming the stunning gemstone.

 

The Role of Climate and Environment

Climate and the environment play a crucial role in turquoise formation. Arid and semi-arid regions with specific geological conditions are most conducive to the formation of this gemstone. The ideal environment for turquoise formation includes:

• Copper-rich host rocks, such as porphyry copper deposits or weathered volcanic rocks.
• Aluminum-bearing rocks, such as feldspar or clay minerals.
• Phosphate-rich groundwater or hydrothermal fluids.
• Arid to semi-arid climate with minimal rainfall and high evaporation rates.

These conditions allow for the chemical reactions necessary for turquoise formation to occur, resulting in the precipitation of this beautiful gemstone in cavities, fractures, and veins within the host rock.

A fine turquoise specimen from Los Cerrillos, New Mexico, US, at the Smithsonian Museum.

Turquoise deposits are found worldwide, each with their unique characteristics. Notable sources include the United States (Arizona, Nevada, New Mexico), Mexico, Chile, Brazil, Iran, China, and Afghanistan.

Interestingly, the name "turquoise" has roots in Middle English, derived from the French "turkeise" and Old French "turqueise," meaning "Turkish." Although in fact, turquoise is not produced in Turkey, the gemstone got its name because ancient Persian turquoise was transported to Europe via Turkey according to legend, forever linking this captivating gem to its historical journey.

 

Colors and Varieties

One of the most captivating aspects of turquoise is its range of colors. While the most desirable color is a vivid, even blue hue, turquoise can also exhibit various shades of green, blue-green, and even yellow-green. Some turquoise specimens may display a matrix, which is the host rock in which the gem formed. The matrix can appear as dark veins or specks, adding visual interest and uniqueness to each piece.

Untreated turquoise, Nevada, US. Rough nuggets from the McGinness Mine, Austin. Blue and green cabochons showing spiderweb feature.

 Several notable turquoise varieties are prized for their exceptional color and quality:

1. Sleeping Beauty Turquoise: Mined in Arizona, it is known for its uniform, intense blue color with minimal matrix. This variety is highly sought-after for its consistency and vibrant hue.
2. Persian Turquoise: Hailing from Iran, it is celebrated for its vibrant robin's egg blue hue. Persian turquoise has a rich history and is often associated with the iconic turquoise domes of Iranian architecture.
3. Kingman Turquoise: Sourced from Arizona, it displays a range of blue and green shades with an attractive matrix. Kingman turquoise is known for its high quality and is often used in Native American jewelry.
4. Carico Lake Turquoise: Originating from Nevada, this variety is recognized for its unique lime green color. Carico Lake turquoise is rare and highly prized by collectors and jewelry enthusiasts.
5. Number 8 Turquoise: Also from Nevada, this variety is distinguished by its striking spider web matrix, which creates an intricate pattern of black veins against the blue-green turquoise background.
6. Tyrone Turquoise: Mined in New Mexico, Tyrone turquoise is known for its vibrant blue-green hues and often features a distinctive matrix. This variety is highly regarded for its quality and beauty.
7. Porcelanato Turquoise: Found in Minas Gerais, Brazil, this variety is known for its unique appearance resembling porcelain. It often features a light to medium blue color with a smooth, uniform texture, making it an attractive option for jewelry and decorative objects.
8. Brazilian Turquoise: Sourced from various states in Brazil, including Minas Gerais, Bahia, and Rio Grande do Sul, Brazilian turquoise offers a range of colors from sky blue to blue-green and green hues. Some notable varieties include Porcelanato Turquoise, Araçuaí Turquoise, and Sao José Turquoise, each with their unique characteristics and color combinations.

 

Natural vs. Treated Turquoise

It is important to note that not all turquoise on the market is entirely natural. Some turquoise may undergo treatments to enhance its color, durability, or overall appearance. Common treatments include:

• Stabilization: Impregnating the porous turquoise with a clear resin or polymer to improve its durability and color.
• Dyeing: Adding dye to the stabilizing material to enhance or change the color of the turquoise.
• Reconstitution: Compressing small fragments of turquoise with a binding agent to create a more solid and uniform material.

While treated turquoise can still be beautiful and valuable, it is essential for buyers to be aware of any treatments and to consider the value and authenticity of natural, untreated turquoise.

 

Grading Turquoise Quality

Turquoise quality is assessed based on several factors, including color, matrix, hardness, and overall appearance. The most desirable turquoise is typically a uniform, intense blue with minimal matrix and no visible imperfections. However, some collectors and enthusiasts appreciate the unique character that a matrix can add to a piece of turquoise.

The Gemological Institute of America (GIA) has developed a grading system for turquoise based on the following criteria:

• Color: The most valuable turquoise is a consistent, vivid blue. Green, blue-green, and yellowish-green hues are less desirable.
• Clarity: High-quality turquoise should be free of visible imperfections, such as cracks, pits, or inclusions.
• Matrix: While some prefer minimal matrix, others appreciate the unique patterns and character it can add to the turquoise.
• Cut: Turquoise can be cut into various shapes, including cabochons, beads, and tablets. A well-executed cut enhances the gemstone's beauty and value.
• Carat weight: Larger pieces of high-quality turquoise are rarer and more valuable than smaller ones.

By considering these factors, buyers can make informed decisions when purchasing turquoise jewelry or loose gemstones.

 

Frequently Asked Questions

1. What gives turquoise its blue color?

The blue color in turquoise is primarily due to the presence of copper in its chemical composition. Copper ions absorb red and green light, reflecting blue wavelengths and giving turquoise its characteristic hue.

2. How can I tell if turquoise is natural or treated?

Identifying treated turquoise can be challenging without proper gemological equipment. However, some signs of treatment include a uniform, artificially vibrant color, a lack of natural matrix, and a lower price compared to natural turquoise of similar size and quality. Always ask for disclosure of any treatments when purchasing turquoise.

3. Is turquoise a birthstone?

Yes, turquoise is a traditional birthstone for December, along with zircon and tanzanite. It is also associated with the zodiac sign of Sagittarius.

4. How do I care for turquoise jewelry?

Turquoise is a relatively soft and porous gemstone, requiring special care to maintain its beauty. Avoid exposing turquoise to harsh chemicals, cosmetics, and extreme temperatures. Clean turquoise jewelry gently with a soft cloth and mild soap and water. Store turquoise pieces separately to prevent scratching or damage.

 

A Gemstone Like No Other

Turquoise is a gemstone that captivates with its enchanting colors and rich history. Its formation is a testament to the complex geological processes that take place beneath the Earth's surface, resulting in a gem cherished by cultures worldwide. From the vivid blues of Sleeping Beauty to the striking green of Carico Lake, the various turquoise colors and varieties offer something for every jewelry lover.

As you explore the world of turquoise, remember that each piece is unique, telling a story of its formation and the journey it has taken to reach you. Whether you are drawn to the classic blue hues or the more unusual green shades, turquoise is a gemstone that will never fail to captivate and inspire.

Be sure to read more of our articles in this series about turquoise, including the stone's cultural significance and history, as well as turquoise's fashion trends, styling and care guidance.