Tiger’s eye (pseudocrocidolite, tiger eye, or tigereye) is a golden-yellow to golden-brown to reddish-brown attractive, popular, yet inexpensive gemstone that exhibits chatoyancy due to the intergrowth of nearly parallel quartz crystals and altered crocidolite fibers, especially limonite.
This chatoyant, translucent, semi-precious metamorphic rock, often banded, is made of quartz with the key element or chemical composition silicon dioxide (SiO2) with inclusions of crocidolite (Na2Fe3Fe2[(OH)Si4O11]2. Some of its uses include making jewelry like bracelets, earrings, necklaces, anklets, and centerpieces for rings, pendants, brooches, etc., and other decorative ornamental objects.
Today we will discuss more about the tiger’s eye gemstone, including how it forms, where it occurs, some of its uses, how much it costs, and much more. Unfortunately, we will not explore any information about its metaphysical, healing, religious, or astrological properties or significance.
However, before that, let us quickly refresh our memory on chatoyancy or the so-called cat’s eye effect. See our post on chatoyancy meaning, causes, and stone examples for details.
Understanding chatoyancy
Chatoyancy is an optical property where an appropriately cut cabochon gemstone, rock, crystal, or mineral reflects a single, narrow streak of bright light with a silky luster that seems to move across its curved surface as you turn it or move the light source. This luminous band of light resembles a cat’s eye pupil that appears as a vertical slit or streak. Thus, the optical phenomenon is sometimes called a cat’s eye effect.
A chatoyant mineral shows this cat’s eye effect, and we can use the cat’s eye adjectively to describe these minerals. For instance, you can have cat’s eye opal, quartz, aquamarine, sapphire, alexandrite, chrysoberyl, etc. When used alone, cat’s eye usually means cymophane, a variety of chrysoberyl with the clearest chatoyancy.
Chatoyancy happens in minerals with a fibrous structure or numerous elongated parallel cavities, fluid-filled channels, or needle-like inclusions that reflect light perpendicular to their orientation.
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What is a tiger’s eye gemstone?
Tiger’s eye refers to a golden-yellow to golden-brown to reddish-brown to orangish-brown popular, attractive, semi-precious quartz, which displays chatoyancy due to altered fibrous crocidolite inclusions. When cut in cabochon, this gemstone reflects a single, narrow streak of a silky lustrous bright band of light or sheen that seems to summit the concave surface as you turn it or move incidence light.
Crocidolite, or blue asbestos, is a fibrous form of riebeckite, a sodic amphibole group mineral. It is usually bluish-gray but might be indigo-blue or leak-greenish and has a lath-shaped needle-like fibrous structure with parallel sides. However, alteration changes it into golden-yellowish or golden-brown.
Tiger’s eye is a kind of cat’s eye or chatoyancy. It refers to a chatoyant quartz (silicon dioxide) with altered crocidolite with a yellowish to golden to brownish color, which resembles the yellowish to anger (yellowish orange) eyes of a tiger which also have a characteristic streak.
Besides this gemstone, you may have the following variations because of crocidolite inclusions:
- Falcon’s or hawk’s eye: If no crocidolite alteration happens, you will end up with the grayish-blue chatoyant gemstone known as falcon’s or hawk’s eye.
- Zebra tiger’s eye or zebra crocidolite: It refers to the chatoyant particolored tiger’s eye gemstone with golden brown and bluish-gray variegation. It happens due to partial alteration of crocidolite.
Lastly, you may also have the grayish-green cat’s eye quartz besides tiger’s and hawk’s eye. It forms due to the inclusion of actinolite, another type of the amphibole group asbestos. The other types are reddish or brownish jasper.
Properties
Some properties of the tiger’s eye include:
- Chemical composition: Silica or silicon dioxide (SiO2) with altered blue asbestos, especially limonite inclusions
- Colors: Golden yellow to golden-brown to brownish red, often banded
- Mohs hardness: 7 Mohs scale
- Luster: Silky
- Fracture: Conchoidal
- Specific gravity: 2.64–2.71
- Diaphaneity: Translucent to nearly opaque
- Tenacity: Brittle
- Refractive index: 1.534 to 1.540
How is the tiger’s eye formed?
There are two explanations behind their formation, i.e., 1) the replacement of altered crocidolite by quartz, a pseudomorphism process, and 2) the crack-seal vein-filling process. Let us explore each of these theories.
1. Silicification or pseudomorphous replacement
Pseudomorphism is the oldest and most common explanation for a tiger’s eye formation, i.e., replacing altered crocidolite while retaining this asbestos’s wavy, nearly parallel fibrous structure or form. Alteration of blue-grayish asbestos will make them turn golden-yellow or golden-brownish due to the formation of mostly limonite, i.e., the hydrated iron (III) oxides. During the process, Fe2+ alters to Fe3+.
Once altered, groundwater containing dissolved silica will infiltrate and replace the fibers, i.e., silicification will occur while retaining some of the hydrous iron oxide impurities and fibrous asbestiform structure. Thus, the gemstone will have subparallel fibrous quartz that reflects light perpendicular to its orientation resulting in chatoyancy and is sometimes known as crocidolite quartz.
The golden-yellow to golden-brown to reddish-brown coloration comes from oxidizing iron to limonite, forming part of the silicified crocidolite.
Sometimes the term griqualandite is given to the yellowish-brown to reddish-brown silicified blue asbestos (crocidolite) chatoyant gemstone, which has silica and ferric hydrate. The name comes from Griqualand, a home to Asbestos Mountains in once Cape Colony in South Africa, where this silicified crocidolite was mined.
2. Crack-seal vein-filling process
Peter Heaney, a Pennsylvania State University mineralogist, and Don Fisher, his co-author, a structural geologist, published a paper in 2003 proposing a new possible way of how a tiger’s or hawk’s eye formed.
Microscope observation revealed that the tiger’s eye of a specimen from South Africa showed nonfibrous tiny quartz columns and speckles of fibrous crocidolite inclusions with no chalcedony or fibrous quartz. The chatoyancy resulted from the inclusion of crocidolite.
Therefore, this gemstone formation didn’t result from the pseudomorphic replacement of altered crocidolite (blue asbestos) by quartz retaining the fibrous form of the asbestos.
A possible method by which tiger’s eye and hawk’s eye form is through the crack-seal vein-filling mechanism. It happens when quartz-rich veins fracture after failing elastic deformation forming a microscopic crack in the middle and upper crust. Afterward, water containing quartz and crocidolite enters the microcrack, and quartz starts growing on the fracture’s surfaces, surrounding, or wrapping growing minute pieces of crocidolite fibers on the crack surface.
The microcrack fills, another one develops, and the process repeats until the tiger’s and hawk’s eye forms. The golden-brownish color results from crocidolite weathering, i.e., iron hydroxides and oxides coats, and it is not weathered; you have the hawk’s or falcon’s eye.
However, Dave V. Wiltschko, a structural geologist at Texas A&M University in College Station, doesn’t seem to agree with the theory. He believes there should be quartz damage from tiny fluid pockets and deformation. The authors never discussed it.
Dyed tiger’s eye
The natural tiger’s eye is yellowish, honey, golden-yellow, yellowish-brown, bronze, golden yellow, and reddish brown, with some specimens particolored. Some may also have blackish bands.
Dying of chalcedony or quartz, including this gemstone with inorganic pigments, is a common and accepted practice that doesn’t require a trade qualification. It doesn’t affect the original properties of the gemstone. Thus, you can get dyed blue, red, green, purple, pink, magenta, fuchsia, dark blue, golden blue, teal, or rainbow tiger’s eye gemstone.
Ox or bull’s eye (heat treated)
Heat treating the golden-brownish or golden-yellow tiger’s eye and a temperature of 400°C will result in reddish-brown chatoyant quartz, often known as the bull’s eye or ox eye. The color change occurs as limonite turns into hematite.
Pietersite
Pieterstite is blue-gray, brownish-red, yellow to brown, or golden-hued brecciated or fractured tiger’s eye variety with crocidolite (amphibole fibers) from Namibia and China.
Uses
Some of the uses of the tiger’s eye are in lapidary work that involves cutting and polishing ornamental objects like making cabochons, engraved gemstones, curved cameos, miniature sculptures, spheres, pendulums, and ashtrays. Also, it makes plugs, pyramids, and heart-shaped, mushroom-shaped ornaments, especially if you have large pieces.
The other use of this gemstone is in making beads, bracelets, anklets, earrings, curved/band rings, chockers, and centerpieces from rings, studs, brooches, and pendants, including faceted ones.
How much is a tiger’s eye worth?
Tiger’s eye prices range from less than a dollar to about $3 per carat for most popular types, making them inexpensive. However, these prices may vary slightly depending on the appearance, size, and origin. Some very rare kinds and larger ones may cost more.
You can buy raw (less appealing uncut and unpolished), tumbled, or cut and polished kinds, and your choice will affect their prices.
How to tell if a tiger’s eye is real or fake?
You should spot a genuine tiger’s eye by looking at its color (yellowish to golden yellow to reddish brown shades) and physical properties. It should have silky luster, conchoidal fracture, a density of 2.64–2.71, and be nearly opaque to translucent. Also, it should be brittle.
Since it has a Mohs hardness of 6.5-7, a knife (Mohs hardness 5.5) shouldn’t scratch it; it should scratch a window or glass plate.
Luckily, unless dyed to deceive you, we don’t know synthetic tiger’s eye gemstones -only alexandrite. You should be able to distinguish these gemstones from synthetic glass. Also, get a trusted jewelry vendor.
Frequently asked questions
Some key sources of tiger’s eye are Griqualand, Hay, Griekwastad, Niekerkshoop, Balloch Mine, and Prieska in Northern Cape, South Africa, and Mount Brockman, Western Australia. Other locations or places where they come from are Bolivia, Burma, Namibia, India, the United States, India, Brazil, China, Canada, Madagascar, and Myanmar.
However, note that the California and Arizona tiger’s eye is a serpentine whose chatoyancy is from fibrous chrysotile, an asbestos form. Montana and Lilly Pad Village in Georgia has these gemstones in the USA.
It is true that blue asbestos is harmful and hazardous and causes asbestosis and mesothelioma. And again, the tiger’s eye has a tiny amount of blue asbestos, but it is not petrified wood or blue asbestos. However, the blue asbestos is locked deep within quartz, i.e., unliberated.
Only free asbestos is dangerous. Thus, these gemstones are safe for the wearer, even if you wear them daily, including raw ones. You can even wash them and put them in the sun (not for long, as prolonged exposure can degrade their quality).
It is a semi-precious metamorphic rock gemstone and not a mineral. Its composition is mainly quartz/silica mineral and has some blue asbestos inclusions.
No. Quartz and blue asbestos in this gemstone are non-magnetic materials. Thus, it is not a magnetic material unless it has hematite. However, tiger iron, which has mainly tiger’s eye, black hematite, and red jasper, is magnetic. Some tiger iron may be magnetic if it has hematite.
References
- Manutchehr-Danai, M. (2009). Dictionary of gems and gemology (3rd ed.). Springer.
- Okrusch, M., & Frimmel, H. (2020). Mineralogy: An introduction to minerals, rocks, and mineral deposits. Springer. https://doi.org/10.1007/978-3-662-57316-7
- Symes, R. F. (2005). Eyewitness Crystal & Gem (1st ed.). DK Pub. (Dorling Kindersley).
- Read, P. G. (2010). Gemmology (3rd ed.). N.A.G.
- Webster, R., & Read, P. G. (2006). Gems: Their sources, descriptions, and identification (6th ed.). Elsevier.
- Mccarthy, T. (2015). Understanding Minerals & Crystals (1st ed.). Struik Publishers (pty) Ltd.
- Heaney, P. J., & Fisher, D. M. (2004). New interpretation of the origin of Tiger’s-Eye: Comment and reply. Geology, 32(1). https://doi.org/10.1130/0091-7613(2003)031%3C0323:NIOTOO%3E2.0.CO;2
- Lubick, N. (2003, April 4). Poking at tiger’s eye. Science. https://www.science.org/content/article/poking-tigers-eye
- Hu, K & and Heaney, P. J. (2010). A microstructural study of pietersite from Namibia and China. GIA. https://www.gia.edu/doc/A-Microstructural-Study-of-Pietersite-from-Namibia-and-China.pdf