Sapphire

Sapphire

   Sapphire, also known as blue sapphire, refers to corundum gemstones in shades of blueranging from deep blue to violet-blue or sky-blue. If the corundum gemstone appears in other colors, it is called a fancy sapphire, and is referred to by its specific color, such as yellow sapphire, pink sapphire, or green sapphire.

The only exception is red corundum, which is given its own distinct name: ruby.

   Mineral Family
       Sapphire, also known as blue sapphire, belongs to the same mineral family as rubythe corundum group. Its chemical formula is AlO (aluminum oxide), and its crystal structure falls under the trigonal system. As a result, sapphire and ruby share the same physical, chemical, and optical properties.

   Sources
      Sapphire deposits in Asia are found in Sri Lanka, Thailand, Myanmar, China, Vietnam, and Cambodia. In Africa, notable sources include Nigeria, Kenya, Tanzania, and Madagascar, the latter of which is emerging as a major producer. In the United States, the most famous sapphire source is Yogo Gulch, known for its beautiful sapphires, although they are typically small and embedded in hard rock, making extraction difficult.

      Sapphires from Australia are generally very dark in color and often show a distinct greenish-blue hue when viewed from different angles. The most famous and highly prized sapphires come from Kashmir and Myanmar (Burma). These sapphires are known for their velvety blue color and high clarity, but today they are extremely rareeven rarer than Burmese rubies.

      Sapphires from Thailand and Cambodia are similar in appearance, usually displaying a deep blue color with relatively uniform saturation. Sri Lankan sapphires tend to be lighter in color and more transparent, often containing needle-like inclusions and veil-like inclusions.

General Properties

    Hardness: 9 on the Mohs scale
    Refractive Index: 1.77
    Specific Gravity: 4.0

   Distinctive Properties
      The blue color of sapphire comes from the presence of iron (Fe²) and titanium (Ti), which substitute for aluminum (Al³) in the crystal structure. A charge transfer between Fe² and Ti helps balance the overall charge to match that of Al³, resulting in the gemstone reflecting blue light.

      If some of the iron ions (Fe²) are oxidized to Fe³, the blue color becomes lighter and brighter. This oxidation can be achieved by heat treatment in the presence of air or oxygen, which facilitates the change in the oxidation state of iron.

   Popular Cutting Styles
      Transparent, high-quality sapphires are typically faceted into various shapes such as round, oval, or heart-shaped cuts. For sapphires with a more opaque or milky appearancesuch as Geuda or star sapphiresthe cabochon cut is preferred to highlight surface effects like asterism. Extremely opaque stones are often carved instead of faceted.

   Popularity in the Gem World
      Sapphire is one of the most widely used and long-admired gemstones in both Europe and Asia. It holds the highest market value among blue-colored gemstones.

   Beliefs
      Sapphire is believed to symbolize truth, loyalty, and sincerity. Often referred to as the gem of heaven, it has long been associated with royalty and high-ranking clergy.

      In ancient European lore, it was believed that the Earth rested upon a giant sapphire, which reflected its deep blue color into the sky. The large blue gemstone set in the British royal crown is also a sapphire, symbolizing the wisdom and power of the reigning monarch.

      Sapphire is the birthstone for September and is traditionally associated with the planet Saturn.

A Buddha figure carved from opaque sapphire

   Care and Maintenance
      Sapphires generally do not require special care, except for those that have undergone treatments. Treated sapphires should be kept away from harsh chemicals during cleaning.

   Enhancement Methods
      Color diffusion is used to improve the stones color or to create a star effect. Heat treatment is applied to modify the color. Additionally, filling with glass, plastic, resin, or other materials may be done to increase transparency, enhance durability, or add weight.

   Synthetic Sapphire
      Most synthetic sapphires are produced using the Verneuil method, which involves sprinkling a mixture of alumina powder and coloring elements into a high-temperature flame. The alumina powder melts and crystallizes on a rotating pedestal to form sapphire crystals.

   Examination
      Synthetic sapphire and fancy sapphire have been produced for a long time. Most synthetic sapphires have deep, vibrant colors, are clean and transparent, and free of inclusions. Therefore, if you see a sapphire that is very clear and clean, its wise to be suspicious.

      Additionally, synthetic sapphires usually have very uniform color from all angles without any color zoning. To be more certain, examine the growth lines under 30x magnification. The gemstone must be positioned correctly since these growth lines are visible only from specific directions.

      Sometimes, the sapphire is immersed in methylene iodide, a liquid with a refractive index close to that of sapphire, to make the growth lines more visible. These growth lines are crystal growth patterns formed on the seed rod, which slowly rotates to encourage crystal formation.

In natural sapphires, these growth lines appear as straight lines, whereas synthetic sapphires often show curved or circular growth lines.

Star sapphires are created through diffusion treatment.

      Besides the growth lines, one should also look for unusual inclusions that are not natural, such as metallic fragments or tiny air bubbles.

Curved growth lines are found in synthetic sapphires, while straight growth lines appear in natural sapphires.

   Comparable Gemstones
      There are only a few natural gemstones that resemble sapphire, such as tanzanite and iolite, though both are still relatively uncommon. Other materials like cz (cubic zirconia) and synthetic substances, such as deep blue cobalt glass, are often used to imitate sapphire.

Sapphire simulants are also found in composite stones, where a colorless, transparent, and less expensive gemstonesuch as quartz, topaz, white sapphire, pale sapphire, or clear glassis glued on top of a dark blue glass or thin sapphire base. These assembled stones closely resemble natural sapphire, especially when the top layer is sapphire, since their physical properties and visible inclusions mimic natural sapphire perfectly.

      Testing assembled stones is easier when they are not yet set in jewelry. Immersing the stone in olive oil or clove oil helps reveal the glued areas more clearly.

   Fancy Sapphires
      Fancy sapphires refer to all sapphires that are not blue or red. Their colors are determined by the type and amount of trace elements that substitute for aluminum in the crystal structure. Sapphires with an opaque or milky appearance typically contain a high number of inclusions. There are many types of fancy sapphires, including:

• Black Sapphire: These sapphires are so dark blue that they appear black and are often called Nilon in Thai. Unlike other black stones such as black spinel or black tourmaline, Nilon is a variety of corundum and is not fully opaque. In Thai literature, this gemstone is poetically described as having a color like a sky covered in thick storm clouds, known as misty black. The black color is caused by a mix of needle-like rutile inclusions and plate-like hematite crystals. Some black sapphires may also show brownish or golden reflections.

• Green Sapphire: Known in Thailand as Kiew Song or green flashing stone, the most famous variety comes from Bang Kacha in Chanthaburi province. These stones are usually deep green with a slight bluish tint and are sometimes referred to as the emerald of Chanthaburi. However, their color is much darker than true emeralds. A notable feature of Bang Kacha sapphires is the presence of color zoning, often referred to locally as stone lines.

• Padparadscha Sapphire: This rare variety has a blend of pink, orange, and yellow tones. The name Padparadscha comes from the Sinhalese word for lotus blossom, reflecting its delicate, mixed coloring. True padparadscha sapphires have a pink base color with hints of orange, yellow, or red.

 
Green sapphire from Bang Kacha, Chanthaburi

   Padparadscha Sapphire
      Padparadscha sapphires always contain a blend of pink and another hueeither orange or yellow may be dominant, but there must always be a visible pink component. Therefore, it is important to understand that padparadscha is not simply an orange sapphire or a pink sapphire, but a unique mix of both colors harmoniously blended.

      Most padparadscha sapphires contain mineral crystal inclusions, and the deeper the color, the more inclusions are usually present. Clean, transparent padparadscha sapphires with vivid and intense color are extremely rare and can be as valuable as fine rubies or blue sapphires.

      Padparadscha was first discovered in Sri Lanka. Later, sapphires with similar orangey-pink hues were found in the Umba Valley in Tanzania, though these tend to lean more toward reddish-orange in tone.


   Pink Sapphire
      Pink sapphires range from pale pink to deep pink, sometimes with a hint of red. As long as the base tone is pink, the stone is classified as a pink sapphire and not a ruby. Most pink sapphires are light in color, with even saturation and little to no color zoning, unlike other fancy sapphires. Vivid, richly colored pink sapphires are highly valuable.


   White Sapphire
      White sapphires are colorless or may have a faint tint of blue, yellow, or pink. Truly pure white sapphires are rare. Due to their hardness and bright sparkle, they are often used as diamond substitutes in jewelry.


   Yellow Sapphire
      Yellow sapphires occur in a range of tones, from pale yellow to more intense hues.

Ceylon Sapphire

   Yellow Sapphire and Heat-Treated Geuda
      Yellow sapphires can range in color from pale buttery tones to medium yellow. In some regions, they are popular substitutes for yellow diamonds. The most sought-after and valuable colors are deep yellow to yellow-orange, often referred to as Mekong Yellow.

      Yellow sapphires from Chanthaburi Province in Thailand often have a greenish tint and are called Nam Taeng (melon water). If the stone displays a golden yellow color, it is referred to as Nam Thong (golden water). Some yellow sapphires are produced by heat-treating green sapphires.

Geuda is a low-quality sapphire from Sri Lanka, typically pale blue or pale yellow with a cloudy or milky appearance due to a high amount of inclusions, especially fine needle-like inclusions. When subjected to high-temperature heat treatment for several hours, these inclusionsmostly rutile needles rich in titanium

dissolve into the crystal, improving transparency.

      During heating, titanium from the rutile combines with iron already present in the stone, resulting in a deeper and more vibrant blue color. This process transforms low-grade Geuda into high-quality sapphire with greater market value.

Chanthaburi, Thailand is world-renowned for its heat treatment of sapphires and is considered one of the most famous locations globally for this specialized gem enhancement.

Greenish-yellow sapphire

Nam Taeng Sapphire from Chanthaburi

   Trapiche Sapphire
      A Trapiche sapphire is a sapphire of any color that displays inclusions arranged in three intersecting rays at approximately 120 degrees, forming a six-rayed star-like pattern. These rays follow the directions of the three crystal axes that lie in the same plane. This distinctive pattern of inclusions is known as the trapiche structure.

      The same phenomenon is also found in trapiche emeralds, where similar inclusions form the same star-like pattern.

      Most trapiche sapphires are opaque, not very clean, and lack brilliance, making them less commonly used in jewelry. However, due to their rarity, they are highly prized by collectors.