Fisher, professor of geosciences, investigated tiger's eye, using light optical microscopes, x-ray diffraction techniques and transmission electron microscopes to determine the origin of the fibrous character that imparts chatoyancy to this gem. Consequently, Wibel's interpretation has endured in standard mineralogy textbooks for 125 years." "Surprisingly, tiger's eye also is one of the few gem materials that has virtually eluded modern micro analysis. "This theory had not been challenged since Wibel suggested it in 1873," Heaney says in a paper in the April issue of the journal Geology. They believed that in tiger's eye, the pseudomorphism went to completion and the rusting of iron in the asbestos caused the golden color. They believed that quartz replaced most of the crocidolite, and the remaining asbestos provided the bluish color. In the late 1800s, geologists thought that tiger's eye and the related blue-green stone, hawk's eye, were quartz replacements of crocidolite - a blue form of asbestos. "When I looked at a thin section, I realized that it was not pseudomorphism." Heaney, associate professor of geosciences. "I looked at tiger's eye because I expected to see pseudomorphism and wanted to understand better how the replacement took place," says Dr. In petrified wood, for example, the material of the tree is replaced by minerals, but the tree shape and even the ring demarcations remain visible. In pseudomorphism, the molecules of an original material are replaced by another material with the physical structure remaining unchanged. Since 1873, geologists have believed that tiger's eye is an example of pseudomorphism. Once considered a highly valued rarity in western Europe, the discovery of large sources in South Africa in the 1880s caused its value to plummet, but today, it is a popular, although inexpensive, stone. The popular stone with its deep brown to gold striations and shimmery glitter adorns jewelry throughout the world. Beauty may be in the eye of the beholder, but when it comes to what gives tiger's eye its beauty, geologists may have been wrong for years, according to Penn State geoscientists. Structure of tiger's eye reevaluated after 125 years
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