Tiger Eye is a captivating gemstone known for its striking appearance and shifting play of light. Its appeal lies in lustrous, wavy bands that resemble a tiger’s eye, making it a popular choice for jewelry and ornamental objects.
Primary Mineral Composition
Tiger Eye primarily consists of silicon dioxide (SiO2), making it a variety of quartz. It is distinguished by fine, parallel fibrous inclusions. These fibers are typically composed of crocidolite, an amphibole mineral. Its unique appearance stems from the alteration and replacement of these initial mineral components.
The Formation Process
Tiger Eye forms through pseudomorphosis, a geological process where one mineral replaces another while retaining its original shape. Fibrous crocidolite forms, then groundwater rich in silica seeps into the rock, dissolving the crocidolite fibers. As the crocidolite dissolves, silica (quartz) crystallizes and fills the void, preserving the original fibrous structure.
Iron within the original crocidolite oxidizes during this replacement process, which imparts the golden-brown and reddish hues to the stone. This preserved fibrous structure is responsible for chatoyancy, or the “cat’s eye” effect. Light reflects off these parallel, microscopic fibers, creating a luminous band that appears to glide across the gemstone’s surface.
Defining Physical Attributes
Tiger Eye exhibits several distinct physical attributes that contribute to its appeal and durability. It registers a hardness of approximately 7 on the Mohs scale, making it suitable for jewelry applications. The stone possesses a silky to vitreous luster, which enhances its visual depth, especially when polished. Its specific gravity generally ranges from 2.64 to 2.71, indicating its density.
Classic Tiger Eye is known for its golden-brown and reddish-brown colors. Blue Tiger Eye, often called Hawk’s Eye, forms when iron oxidation is less pronounced, retaining more of the original crocidolite’s blue-gray color. Red Tiger Eye can occur naturally from further oxidation or through gentle heat treatment of the golden variety.
Global Occurrence
Tiger Eye deposits are found in various locations around the world, reflecting the widespread geological conditions necessary for its formation. South Africa is a historically significant and major source, particularly the Northern Cape Province. High-quality material, including both golden-brown and blue varieties, is often mined in this region.
Australia is another prominent source, with deposits in Western Australia known for producing golden-brown Tiger Eye and unique patterns like Marra Mamba. Other notable occurrences include parts of the United States, such as California and Arizona, as well as Brazil, India, Namibia, Myanmar, China, and Spain. These diverse geographical sources contribute to the global availability of this captivating gemstone.