Blue Tiger's Eye

Hardness: 6.5-7 on Mohs scale. Color: Predominantly blue, varying from deep navy to vibrant teal, often with streaks or bands of darker blue or black. Luster: Silky to vitreous. Crystal structure: Trigonal (quartz), but microcrystalline with fibrous inclusions. Exhibits chatoyancy (cat's eye effect) due to parallel intergrowth of quartz and altered amphibole fibers. Opaque. Specific Gravity: 2.64-2.71.

Blue Tiger's Eye forms when the fibrous mineral Crocidolite (a type of asbestos) is replaced by quartz while retaining its original fibrous structure. This process is known as pseudomorphism. The blue color is often attributed to the presence of unoxidized Crocidolite fibers or specific iron inclusions. Geologically, it forms in metamorphic environments, typically found in banded iron formations. The age varies depending on the specific deposit, but these processes generally occur over millions of years.

Primarily used in jewelry for beads, cabochons, and carvings due to its striking chatoyancy and color. It's popular for bracelets, necklaces, and pendants. Also collected by mineral enthusiasts. It is believed by some to have metaphysical properties, such as aiding in stress reduction, clear communication, and providing protective energy.

Blue Tiger's Eye is also known as Hawk's Eye. It is a precursor to the more commonly known golden Tiger's Eye. When the iron in the crocidolite further oxidizes, it can turn the blue color to the golden-yellow or reddish-brown of regular Tiger's Eye. The chatoyancy effect is what makes this stone so visually appealing and is caused by the light reflecting off the parallel fibrous inclusions within the quartz. It's part of the quartz family and is relatively durable.

In the field, Blue Tiger's Eye is identified by its distinct blue color and the characteristic silky chatoyancy (a shimmering band of light that moves across the surface as the stone is rotated). It often occurs in massive forms, sometimes within layers of other metamorphic rocks. Common locations include South Africa, Australia, India, Thailand, and the USA (Arizona). For collectors, identifying the quality depends on the intensity of the blue color and the prominence and sharpness of the chatoyancy.