Tiger’s Eye is a distinctive gemstone, recognizable by its shimmering, silky appearance and characteristic golden-brown coloration. It is primarily a variety of chalcedony quartz, meaning its chemical composition is silicon dioxide. The stone’s unique visual effect, known as chatoyancy, is a luminous band of light that moves across the surface, similar to the slit eye of a cat. It is a popular material used globally for jewelry, cabochons, and various forms of ornamentation.
Geological Context of Tiger’s Eye Formation
Tiger’s Eye develops through a geological process known as pseudomorphism. This occurs when one mineral is chemically replaced by another while retaining the original mineral’s physical shape. The precursor mineral is crocidolite, which is a fibrous, blue-gray asbestos.
Silica-rich fluids infiltrate the host rock and gradually dissolve the crocidolite fibers. The quartz then crystallizes to fill the voids, replacing the original mineral. The replacement is precise, preserving the sub-parallel, fibrous structure of the crocidolite. The golden-brown hue of the typical Tiger’s Eye results from the oxidation of iron within the crocidolite fibers, transforming it into iron oxides like limonite. This formation process requires specific metamorphic conditions and is often associated with ancient banded iron formations.
Primary Commercial Sources
South Africa is the most significant source of Tiger’s Eye and remains the dominant supplier to the world market. The majority of the global commercial supply originates from the Griqualand West area in the Northern Cape Province. This region is part of the Asbestos Hills Subgroup, which contains the unique geological formations necessary for the stone’s creation.
The immense scale of the deposits discovered here in the late 19th and early 20th centuries transformed Tiger’s Eye from a rare, expensive stone into an affordable material. The South African material is known for its high quality and distinct, vibrant golden-brown chatoyancy. Mining operations extract the stone from specific layers within the iron-rich bedrock.
The deposits often occur in veins within quartzose schists, a metamorphic rock type. Although the mining of crocidolite asbestos has been banned in South Africa, the extraction of Tiger’s Eye continues. This is because the crocidolite within the stone has been largely silicified and altered, though its proximity to asbestos fibers remains a regulatory consideration.
Secondary and Minor Deposits
While South Africa is the principal source, other countries contribute to the global supply, often offering unique color variations. Australia is a notable secondary source, particularly Western Australia, where the material is sometimes found as a component of the ornamental rock known as Tiger Iron. This rock is a banded combination of golden Tiger’s Eye, red jasper, and black hematite.
Brazil also has deposits of the stone, as do parts of India, which add to the overall commercial volume. In the United States, small deposits have been identified in states like Arizona and California. Note that some material marketed from these regions is actually a different form of chatoyant serpentine.
Related Varieties and Minor Sources
Namibia is recognized for a distinct variety called Pietersite, which is a brecciated form of chatoyant chalcedony that includes amphibole fibers. This material often exhibits swirling patterns of blue, gold, and red. The blue variety of Tiger’s Eye, which has less oxidized iron, is sometimes called Hawk’s Eye. If the stone is naturally or heat-treated to a darker red or reddish-brown color, it is often called Ox Eye.
Other minor sources of the gemstone include:
- China
- Myanmar (Burma)
- Spain