STAR GEMSTONES
Chatoyancy
A cats eye gemstone refers to a gem that displays a distinct band of light across its surface when exposed to light. This optical phenomenon is known as chatoyancy. It occurs when light reflects off parallel inclusions or fibrous structures within the gemmost prominently under sunlight or direct artificial lightcreating the appearance of a narrow, glowing line reminiscent of a cat's eye. Even when the stone contains a mixture of various minerals, this light effect can still be visible and is recognized as a sign of the cats eye phenomenon.
While many gemstones can exhibit chatoyancy, only a few types are commonly used and valued in gemology. The term "cats eye" on its own specifically refers to chrysoberyl cats eye, which is highly prized for its sharp, golden beam of light that closely resembles a cats eye. When other types of stones exhibit this effect, their names are always prefixed to avoid confusionfor example, "cats eye quartz," "cats eye tourmaline," or "cats eye sapphire." Only chrysoberyl is referred to simply as "cats eye" without further clarification.
In Thai tradition, the cats eye gemstone is one of the nine auspicious gems, known as Navaratna. It is listed as the ninth gem and is referred to in the phrase "Phaitoon necklace," where phaitoon signifies the cats eye appearancea gemstone bearing a luminous, eye-like stripe, like a protective eye worn as an amulet.
Mineral Family
Cats eye belongs to the chrysoberyl mineral family, the same family as alexandrite. Its chemical formula is BeAlO. Chrysoberyl crystals form in the tetragonal crystal system, which features a square base structure.
Sources
Cats eye gemstones are primarily found in Sri Lanka, India, and Brazil.
General Properties
- Hardness: 8.5 on the Mohs scale
- Refractive Index: 1.741.75
- Specific Gravity: 3.71
Distinctive Characteristics
Cats eye is considered a relatively hard gemstone, comparable to sapphire. It comes in a variety of colors, such as green, yellowish-green, yellow, light brown (resembling honey), brown, and even nearly black. High-quality cats eye stones are typically semi-transparent with a silky luster. They display a sharp, narrow band of lightknown as the cats eye effectthat appears to glide across the surface of the gem as it is rotated. Some stones may even show a double eye, with two distinct light bands.
The phenomenon of chatoyancy (cats eye effect) is caused by inclusions within the gemstone that are aligned in one direction, similar to the way threads are woven uniformly in fabric, allowing light to reflect as a band. These inclusions are typically needle-like crystals or flat, tube-like cavities that are microscopically aligned parallel to the crystal's axis.
Importantly, the glowing band does not result merely from surface reflection; instead, it comes from light reflecting off internal inclusions throughout the stone. As a result, when the gem is rotated, the light band appears to move with the viewers eyemuch like a real cats eye that seems to follow you wherever you go.
Popular Cutting Style
Cats eye gemstones are typically cut in a cabochon shape to best highlight the cats eye effect. This domed form enhances the visibility and sharpness of the light band across the stones surface.
Popularity in the Gem World
In reality, cats eye gemstones are quite rare, which makes them less commonly seen or recognized in the broader gem market. Their quality is primarily judged by the sharpness and clarity of the cats eye line, followed by the transparency of the stone itself. Due to their rarity, high-quality specimens are highly sought after by collectors. Especially valuable are cats eye alexandrites, which not only exhibit the cats eye effect but also display color changethese can command prices second only to ruby and sapphire.
Beliefs and Symbolism
In ancient times, cats eye was believed to be a sacred protective stone, guarding the wearer from evil and misfortune. Its mystical reputation stems from the gemstones unique visual effectthe way the light band shifts and appears to follow the viewers gaze, much like the watchful eye of a cat, always alert to danger.
Care and Maintenance
Cats eye is a hard and relatively tough gemstone, making it suitable for cleaning with warm water and even ultrasonic cleaners. It is chemically stable and does not react with most substances. However, if the stone has internal fractures or inclusions, its best to avoid ultrasonic cleaning, as it could worsen the damage.
Quality Enhancement
Currently, no enhancement methods are used to improve natural cats eye gemstones.
Synthesis
Synthetic color-change cats eye gemstones have been produced and are available on the market.
Comparable Gemstones
Many types of gemstones can exhibit the cats eye effect, including apatite, quartz, sillimanite, diopside, gypsum, moonstone, ulexite, tourmaline, and even jade. However, most of these are softer stones, making them more prone to scratching and damage.
Among these, two types are most commonly seen and widely available: cats eye quartz and sillimanite-based cats eye stones.
- Tigers Eye and Hawks Eye are part of the quartz family.
-Tigers Eye typically has a yellowish-brown to greenish-brown color.
-Hawks Eye ranges from deep green to black and is generally opaque with a silky, fibrous luster. When cut into a cabochon, these stones display a light band similar to the eye of a tiger or hawk. The cats eye effect in these gems results from silica and iron oxide replacing the fibrous structure of crocidolite (a type of asbestos mineral), while maintaining its linear formation.
Tigers eye is generally found in larger sizes and has a more opaque body compared to chrysoberyl cats eye. It is widely available around the world and is considered a common and affordable gemstone.
tiger' eye Hawk" eye
Hawks Eye (Fibrolite)
Fibrolite is a gemstone belonging to the sillimanite mineral group. The cats eye effect in fibrolite occurs naturally due to the crystals internal structurecomposed of fine, needle-like white fibers aligned in parallel, resembling silk threads.
Fibrolite comes in a variety of colors, including white, blue, grayish-green, greenish-brown, and pale to deep green. Its hardness ranges from 6 to 7.5 on the Mohs scale, which is softer than chrysoberyl cats eye.
Major sources of fibrolite include Myanmar, Kenya, India, Sri Lanka, Italy, Germany, Brazil, and the United States.
Fibrolite
